We investigated the effects of indium doping on the superconducting properties of YBCO sintered samples and thin films. In sub(2)O sub(3)-doped YBCO and YBa sub(2)Cu sub(3-x)In sub(x)O sub(y) sintered samples showed a gradual decrease in the critical temperature (T sub(c)) with increasing indium content; however, a T sub(c) value above 80 K was maintained even up to 30 vol.% addition and x = 0.4, respectively. Ba sub(3)Cu sub(3)In sub(4)O sub(12) was detected by X-ray diffractometry and energy-dispersive X-ray spectroscopy as a reaction product for both sintered samples. The normalized J sub(c) under a magnetic field of 0.1 T showed a maximum at x = 0.3. Indium-doped YBCO films prepared by pulsed laser deposition showed a similar dependence of T sub(c) on indium content as the sintered samples.