Formation of powders and electromechanical coupling factor of $Pb(Mn_{1/3} Sb_{2/3})_{0.08} Ti_{0.495}Zr_{0.425}O_3$ by hydro-thermal synthesis are described. The hydrothermal reactions each were accomplished at 12$0^{circ}C$~25$0^{circ}C$ for 5hours and sintering was accomplished at 1, .20$0^{circ}C$ for 1hours. The PZT powders by hydrothermal synthesis were formed above 16$0^{circ}C$ and the forms were cubic types. The ratio of grain size of sintered sample to powder was slowly decreased with the rising of hydrothermal reactino temperature but decreased rapidly above 22$0^{circ}C$ Sintering density was decreased with the rising of hydrothermal reaction temperature above 16$0^{circ}C$ but dielectric constant was increased. Electromechanical coupling factor $K_P$ was almost constant at 16$0^{circ}C$~24$0^{circ}C$ range and the value of $K_P$ was about 0.43-0.45