This paper reports two-step ultrasonic method for in-situ synthesis of PMMA/ZnO nanocomposites. First step comprises nanoscale ZnO synthesis through ultrasound- assisted in-situ hydrolysis of zinc acetate. In second step, PMMA/ZnO nanocomposites have been synthesized via ultrasound-assisted in-situ emulsion polymerization in presence of native ZnO particles (1-5 wt%, without surface modification). Approx. 10 x -enhancement in polymerization kinetics is obtained. Properties of nanocomposites for different ZnO loadings are: particle size = 77.7-109.7 nm, maximum degradation temperature = 386.4 degrees C, maximum glass transition temperature = 122.5 degrees C, UV-visible absorption band width = 350-375 nm, electrical conductivity = 0.028-0.207 mu S/cm, tensile strength = 25.8-36.57 MPa, Young's modulus = 1.09-1.47 GPa, percentage elongation = 10.98-17.56%. These enhanced properties (as compared to previous literature) are essentially attributed to uniform dispersion of ZnO in polymer matrix due to intense micro-convection generated by sonication. This results in strong interfacial interactions and adhesion between phases with increased crystallinity. (C) 2016 Elsevier Ltd. All rights reserved.