The hydrothermal synthesis of lead zirconate titanate (PZT) powder with acicular morphology using organic mineralizer, tetramethylammonium hydroxide pentahydrate (TMAH), has been investigated. The TMAH concentration and reaction time have a pronounced effect on the phase composition and morphology of the resultant powders. At 150 degreesC phase pure PZT was obtained after 24 h in 0.5 m TMAH solution, and after 12 h in 1 m TMAH solution. TMAH concentrations lower than 0.5 m do not produce the PZT phase. At all TMAH concentrations, the appearance of a fibrous intermediate phase, Zr-modified tetragonal PX-phase PbTiO3 is observed at the early stage of the hydrothermal process. Depending on the TMAH concentration, the intermediate either dissolves to form cube-shaped PZT (TMAH concentrations of 1-4 m) or transforms in situ to acicular PZT powder using its fibrous morphology as a template (TMAH concentrations of 0.5-0.75 m).