This study presents a step-by-step method for reading and interpreting FTIR spectra of organic materials, with a focus on identifying chemical bonds and structures. The objective is to provide a clear guide for beginners in understanding FTIR data, comparing results with literature. The analysis covers the mid-IR spectrum, divided into four regions: single bond (2500-4000 cm⁻¹), triple bond (2000-2500 cm⁻¹), double bond (1500-2000 cm⁻¹), and fingerprint (600-1500 cm⁻¹). Each region is explained with specific absorption bands and their corresponding functional groups. The study uses Lumbricus rubellus (LR) as a complex organic material example, analyzing its FTIR spectra after heating at various temperatures to observe structural changes. The results show that LR contains high levels of protein, fat, and amino acids, making it a complex organic material. The FTIR analysis of LR microparticles revealed changes in the FTIR peaks after heating, indicating structural transformation. The study also compares FTIR results with known organic compounds, such as 2-propanone and toluene, demonstrating how to interpret their spectra. The findings suggest that FTIR is a valuable tool for analyzing organic materials, providing insights into their chemical composition and structure. The study concludes that the step-by-step method for interpreting FTIR spectra is effective for understanding complex organic materials and can serve as a reference for students and researchers.This study presents a step-by-step method for reading and interpreting FTIR spectra of organic materials, with a focus on identifying chemical bonds and structures. The objective is to provide a clear guide for beginners in understanding FTIR data, comparing results with literature. The analysis covers the mid-IR spectrum, divided into four regions: single bond (2500-4000 cm⁻¹), triple bond (2000-2500 cm⁻¹), double bond (1500-2000 cm⁻¹), and fingerprint (600-1500 cm⁻¹). Each region is explained with specific absorption bands and their corresponding functional groups. The study uses Lumbricus rubellus (LR) as a complex organic material example, analyzing its FTIR spectra after heating at various temperatures to observe structural changes. The results show that LR contains high levels of protein, fat, and amino acids, making it a complex organic material. The FTIR analysis of LR microparticles revealed changes in the FTIR peaks after heating, indicating structural transformation. The study also compares FTIR results with known organic compounds, such as 2-propanone and toluene, demonstrating how to interpret their spectra. The findings suggest that FTIR is a valuable tool for analyzing organic materials, providing insights into their chemical composition and structure. The study concludes that the step-by-step method for interpreting FTIR spectra is effective for understanding complex organic materials and can serve as a reference for students and researchers.