This paper reports the particle and crystallite size characterizations of mechanically alloyed Ba(1-x)SrxTiO3 (BST) with x = 0.3 and 0.7 prepared with the assistance of a high-power sonicator. Analytical grade BaCO3, TiO2 and SrCO3 precursors with a purity of greater than 99 wt.% were mixed and milled using a planetary ball mill to a powder weight ratio of 10:1. Powders obtained after 20 hours of milling time were then sintered at 1200°C for 4 hours to form crystalline powders.These powders were further treated ultrasonically under a fixed 6.7 gr/l particle concentration in demineralized water for 1, 3, 5, 7 hours and a fixed ultrasonic irradiation time of 1 hour to the dispersion of 6.7; 20; 33.3 gr/l concentrations. As to the results of crystallite size characterization, it is demonstrated that the mean crystallite size of BST with x = 0.3 and 0.7 undergo a slight change after the first 1 hour irradiation time and then remain almost unchanged. This was in contrary to the particle size in which the mean particle size of BST with x = 0.3 increased from 765 nm to 1405 nm after 7 hours irradiation time, while that of x = 0.7 increased from 505 nm to 1298 nm after 3 hours and then reduced back to the initial size after 7 hours ultra sonication time. The increase in particle size was due to large of cohesive forces among fine particles. It is also demonstrated that the concentration of particles in a dispersion with anionic surfactant do not effective to reduce the particle sizes ultrasonically. Nanoparticles with the mean size respectively 40 and 10 times larger than their respective crystallite size were successfully obtained respectively in x = 0.3 and x = 0.7.