Background: An effective polymer gel dosimeter can be fabricated by varying the composition of its chemical components. Materials and Methods: The MAGAT gel dosimeter formulations that used different compositions of Methacrylic acid (MAA) and gelatin were extensively investigated in the present study according to the R2–dose response and R2–dose sensitivity. The irradiation of MAGAT gel was performed by 6-MV photon beam at a dose range 1 to 10 Gy and was imaged by 1.5T Magnetic Resonance Imaging (MRI). The dose response of MAGAT gel dosimeter was obtained from spin-spin relaxation rate (R2) of MRI signal. Results: The MAGAT gel dosimeter composed of 5% gelatin and 6% MAA gave the highest sensitivity (1.1180            s^-1Gy^-1). Conclusion: Understanding the effects of the compositional changes will help to clarify the mechanisms involved in the dose response of the MAGAT gel dosimeter.