Microplastics are emerging contaminants that undergo aging under environmental conditions such as sunlight, temperature, and biological activity. Aging changes microplastic properties, including toxicity, requiring advanced analysis methods. This review discusses methods for analyzing aged microplastics, focusing on aging processes, qualitative identification, quantitative characterization, and chemometrics. Qualitative identification uses mechanical, thermal, and spectral techniques like FTIR, Raman, and CARS. Quantitative methods include microscopy and mass spectrometry. Aging causes physical and chemical changes, such as surface roughness, biofilm formation, and oxidation. Infrared and Raman spectroscopy are effective for chemical identification in complex samples. Combining techniques improves detection accuracy. Aging alters microplastic properties, including mechanical and thermal characteristics, which help differentiate aged from pristine microplastics. Semi-crystalline and amorphous polymers have different aging behaviors. Amorphous polymers degrade faster, while semi-crystalline ones are more resistant. Aging increases oxygen content and changes polymer chain structures. The glass transition temperature decreases with aging, indicating molecular weight reduction and chain degradation. Crystallinity increases due to photo- or thermo-oxidation. Mechanical properties change, affecting polymer chain integrity and microplastic formation. Thermal analysis, including thermogravimetric analysis and differential scanning calorimetry, helps identify microplastics by measuring decomposition and melting temperatures. Pyrolysis gas chromatography-mass spectrometry (Pyr-GC/MS) identifies thermal degradation markers. Spectral techniques like FTIR and Raman spectroscopy provide molecular information. FTIR measures surface chemical changes, while Raman identifies polymer types. However, overlapping signals can reduce identification accuracy. Customized spectral databases improve identification of aged microplastics. Fluorescence lifetime imaging microscopy (FLIM) uses fluorescence lifetimes to distinguish microplastics. Phasor analysis helps differentiate microplastics based on their fluorescence characteristics. Laser-induced breakdown spectroscopy (LIBS) identifies polymer types through elemental emission lines. Statistical methods and chemometric tools enhance discrimination. Raman spectroscopy, while useful for polymer identification, is less effective for assessing degradation. CARS and stimulated Raman scattering microscopy offer rapid, sensitive identification in complex samples. Fluorescent tracers can track microplastic movement in aquatic environments. LIBS provides fast elemental analysis, but similar spectra make differentiation challenging. Overall, a combination of techniques is essential for accurate microplastic analysis.Microplastics are emerging contaminants that undergo aging under environmental conditions such as sunlight, temperature, and biological activity. Aging changes microplastic properties, including toxicity, requiring advanced analysis methods. This review discusses methods for analyzing aged microplastics, focusing on aging processes, qualitative identification, quantitative characterization, and chemometrics. Qualitative identification uses mechanical, thermal, and spectral techniques like FTIR, Raman, and CARS. Quantitative methods include microscopy and mass spectrometry. Aging causes physical and chemical changes, such as surface roughness, biofilm formation, and oxidation. Infrared and Raman spectroscopy are effective for chemical identification in complex samples. Combining techniques improves detection accuracy. Aging alters microplastic properties, including mechanical and thermal characteristics, which help differentiate aged from pristine microplastics. Semi-crystalline and amorphous polymers have different aging behaviors. Amorphous polymers degrade faster, while semi-crystalline ones are more resistant. Aging increases oxygen content and changes polymer chain structures. The glass transition temperature decreases with aging, indicating molecular weight reduction and chain degradation. Crystallinity increases due to photo- or thermo-oxidation. Mechanical properties change, affecting polymer chain integrity and microplastic formation. Thermal analysis, including thermogravimetric analysis and differential scanning calorimetry, helps identify microplastics by measuring decomposition and melting temperatures. Pyrolysis gas chromatography-mass spectrometry (Pyr-GC/MS) identifies thermal degradation markers. Spectral techniques like FTIR and Raman spectroscopy provide molecular information. FTIR measures surface chemical changes, while Raman identifies polymer types. However, overlapping signals can reduce identification accuracy. Customized spectral databases improve identification of aged microplastics. Fluorescence lifetime imaging microscopy (FLIM) uses fluorescence lifetimes to distinguish microplastics. Phasor analysis helps differentiate microplastics based on their fluorescence characteristics. Laser-induced breakdown spectroscopy (LIBS) identifies polymer types through elemental emission lines. Statistical methods and chemometric tools enhance discrimination. Raman spectroscopy, while useful for polymer identification, is less effective for assessing degradation. CARS and stimulated Raman scattering microscopy offer rapid, sensitive identification in complex samples. Fluorescent tracers can track microplastic movement in aquatic environments. LIBS provides fast elemental analysis, but similar spectra make differentiation challenging. Overall, a combination of techniques is essential for accurate microplastic analysis.