This study reports the first experimental investigation of isotope effects on the thermal properties of graphene. Isotopically modified graphene with varying percentages of 13C was synthesized using chemical vapor deposition (CVD). The thermal conductivity (K) of isotopically pure 12C (0.01% 13C) graphene was measured to be higher than 4000 W/mK at 320 K, more than twice that of a 50:50 mixture of 12C and 13C. The experimental results agree well with molecular dynamics (MD) simulations, corrected for long-wavelength phonon contributions via the Klemens model. The study shows that the isotope composition significantly affects the thermal conductivity of graphene, primarily through phonon mass-difference scattering. The thermal conductivity of graphene is influenced by the phonon scattering rates from point defects and anharmonic phonon Umklapp processes. The isotope effects in graphene are particularly important for understanding its thermal properties and for developing theories of heat transport in low-dimensional systems. The study also demonstrates that the thermal conductivity of isotopically modified graphene can be significantly enhanced, with the isotopically pure 12C graphene showing a 58% increase in thermal conductivity compared to natural abundance graphene. The results are supported by MD simulations and Raman spectroscopy measurements, which confirm the high quality of the isotopically modified graphene. The study highlights the importance of isotope effects in understanding the thermal properties of 2D materials and provides valuable insights for the development of thermal management technologies in nanoelectronics.This study reports the first experimental investigation of isotope effects on the thermal properties of graphene. Isotopically modified graphene with varying percentages of 13C was synthesized using chemical vapor deposition (CVD). The thermal conductivity (K) of isotopically pure 12C (0.01% 13C) graphene was measured to be higher than 4000 W/mK at 320 K, more than twice that of a 50:50 mixture of 12C and 13C. The experimental results agree well with molecular dynamics (MD) simulations, corrected for long-wavelength phonon contributions via the Klemens model. The study shows that the isotope composition significantly affects the thermal conductivity of graphene, primarily through phonon mass-difference scattering. The thermal conductivity of graphene is influenced by the phonon scattering rates from point defects and anharmonic phonon Umklapp processes. The isotope effects in graphene are particularly important for understanding its thermal properties and for developing theories of heat transport in low-dimensional systems. The study also demonstrates that the thermal conductivity of isotopically modified graphene can be significantly enhanced, with the isotopically pure 12C graphene showing a 58% increase in thermal conductivity compared to natural abundance graphene. The results are supported by MD simulations and Raman spectroscopy measurements, which confirm the high quality of the isotopically modified graphene. The study highlights the importance of isotope effects in understanding the thermal properties of 2D materials and provides valuable insights for the development of thermal management technologies in nanoelectronics.