Lead zirconate titanate solid solution (PZT) was synthesized in potassium hydroxide (KOH) solution under hydrothermal conditions. The relationship between the morphology of the products and the concentrations of starting materials and of KOH were investigated. At 150°C, at least 100mol·m^-3 of PbO and 2000mol·m^-3 of KOH was necessary to form cubelike PZT particles. A higher KOH concentration reduced the size of PZT particles. In order to form PZT nuclei, Pb concentration must be increased supersaturation with respect to PZT. The Pb concentration is restricted by the saturation of PbO which depends on KOH concentration. Therefore the number of nuclei was determined by the KOH concentration when undissolved PbO solid existed at the PZT nucleation stage. Undissolved PbO acted as the buffer of the precipitation of PZT, and PZT particles grew by consuming the Pb supplied from the dissolved PbO. The morphology and the size of PZT particles can be controlled by the amount of PbO and the KOH concentration.