A formula for predicting the stress effect on the electromagnetic resonances of dielectric resonators is obtained by applying a perturbation method to the three‐dimensional Maxwell’s equations in which the dielectric permittivity tensor is perturbed by the applied stress (or strain) field through the piezo‐optic effect. The dielectric resonator, which is surrounded by infinite free space, can be isotropic or anisotropic and of arbitrary shape. By using previously obtained two‐dimensional closed‐form solutions as the approximate unperturbed solutions, stress effect on the electromagnetic resonances in a dielectric circular disk is studied. Frequency changes of both the transverse electric and transverse magnetic modes are computed for disks of gallium arsenide and under three cases of loading: (1) a pair of diametral forces, (2) steady vertical acceleration, and (3) steady horizontal acceleration. In the latter two cases, the bottom face of the disk is supported by a rigid base. ©1996 American Institute of Physics.