The effect of gamma-irradiation and silver doping on the properties of YBCO superconductors has been studied by electrical resistance measurements and x-ray diffraction techniques. The zero-resistance superconducting transition temperature of (YBCO)(1-x)Ag-x systematically increase by about 2 K with an increase of Ag content up to x = 0.04. Further increase in Ag content decreases the transition temperature. The normal-state resistance decreases up to a factor of 3.4 with an increase of Ag content. No significant change in the transition width has been observed due to silver addition up to x = 0.30. Undoped YBCO and the Ag-doped specimens of (YBCO)(1.96)Ag-0.04 were irradiated with gamma-rays up to an integrated gamma-dose of 77 MR. The normal-state resistance of the specimens gradually increases and the transition temperature slightly decreases with increase of gamma-dose. The intensities of the x-ray diffraction peaks of the monolayers of the sample powders decrease with gamma-irradiation without noticeable change of diffraction angles or peak widths. These observations indicate that the high-T-c supconductor YBCO is quite sensitive to gamma-irradiation but drastic lattice expansion does not occur up to a gamma-dose of 77 MR.