We report a synergetic effect of the sensitivity to temperature at different strains on a doped PMMA step-index fiber. The Bragg grating was initially recorded with the phase mask technique using a 325 nm HeCd laser with a central wavelength of 1537 nm. The strain sensitivity of the grating was evaluated applying different strains on the grating in the elastic regime and when it was stretched beyond the elastic limit resulting in a permanent wavelength shift of 20 nm. In order to evaluate the dependence of the Bragg wavelength on temperature sensitivity the grating was placed in a climatic chamber, where the relative humidity was kept constant (50%RH) and the temperature ranged from 30ºC to 60ºC. This test was performed with two different strains (0.13% and 0.35%). During the experimental tests two silica optical fibers were used to remove the deformation effects of the support, one as a temperature sensor and another as temperature and support’s deformation sensor. Results show that the strain sensitivity decreased when the fiber was in the plastic regime and also that the temperature sensitivity depends on the strain applied to the grating.