The large bulk high-Tc YBa2Cu3O7−x (YBCO) superconductor samples were prepared by plastic-forming method. We examined the effects of the solvent and the crystallinity of YBCO powder on the composition, crystallinity, and superconducting properties of YBCO sheet samples (sample size: 50 mm × 50 mm× 3 mm). By changing the solvent from water to turpentine oil, the leaching of Ba2+ ions from YBa2Cu3(OH)y multimetallic hydroxide particles used as an inorganic binder and the YBCO powder were reduced. This results in the composition of the grain boundaries of fired YBCO sheet samples to be the same as the composition of YBa2Cu3(OH)y multimetallic hydroxide particles. Changing nondoped YBCO powder prepared by sintering to 5 wt% Pt-doped YBCO powder prepared by melt texturing, Jc value of YBCO sheet samples changed from about 700 to 6,106 A/cm2 at 77 K.