Fiber Bragg grating was written in hydrogenated multimode fiber, and the temperature sensing properties of multimode fiber gratings are investigated experimentally and theoretically in this paper. Experimental results show that the Bragg wavelength of grating in multimode graded-index fiber is linearly dependent on its temperature; and its repeatability is good. The measured temperature sensitivity of each reflection peak is equal to 0.0098 nm/℃; the temperature sensitivity attained from experimental data is tallies with theoretical analysis. The characteristics are similar to that of a conventional Bragg grating in single-mode fiber. So the multimode fiber grating may replace single-mode fiber grating to produce fiber sensors. The experimental results can also provide guidance for further studying on multimode fiber Bragg gratings.