[ $Ba(Mg_{1/3}Ta_{2/3})O_3$ ] nanoparticles were synthesized in water solution under mild temperature and pressure conditions by precipitation from $Ba(NO_3),;Mg(NO_3)_2{cdot}6H_2O;and;TaCl_5$ with aqueous potassium hydroxide. The average size and distribution of the synthesized $Ba(Mg_{1/3}Ta_{2/3})O_3$ nanoparticles were below 100 nm and broad, respectively. The phase of synthesized particles was crystalline reacted at $170^{circ}C$ for 4 h. The characterization of $Ba(Mg_{1/3}Ta_{2/3})O_3$ nanoparticles were studied using XRD, SEM, and TEM.