Specimens of high-T(c) superconductors, YBCO and (YBCO)1.96 Ag0.04, were irradiated with gamma-rays up to an integrated dose of 77 MR. Electrical resistance vs temperature and the X-ray diffraction patterns of the monolayers of the sample powders were obtained before and after the irradiations. The normal state resistance of the pure and Ag-doped YBCO specimens gradually increase as the gamma-dose increases. The intensities of the X-ray diffraction peaks of the monolayers of the YBCO powders decrease with gamma-irradiation without significant change of diffraction angles or peak widths. The zero resistance transition temperature of the Ag-doped YBCO specimens decreases by about 0.5% with gamma-irradiation at 77 MR. These observations indicate that the high-T(c) superconductor YBCO is quite sensitive to gamma-irradiation but drastic lattice expansion does not occur up to a gamma-dose of 77 MR.