The present study reports ultrasound-assisted biodiesel synthesis using blended feedstock of non-edible oils and commercial immobilized lipase from Thermomyces lanuginosus. Optimum process parameters obtained using Box-Behnken statistical design were as follows: alcohol/oil molar ratio = 7.64:1, enzyme loading = 3.55% (w/w) and temperature = 36 degrees C, conversion = 90%. Sonication of reaction mixture resulted in lowering of activation energy to 100.4 kJ/mol (from 124.4 kJ/mol under mechanical agitation). Addition of water to reaction mixture (10% v/v) not only boosted biodiesel yield from 90% to 94% but also lowered activation energy to 78.7 kJ/mol. Analysis of reaction kinetics using ordered Bi-Bi model revealed drastic rise (similar to 1.6 x) in reaction velocity with concurrent changes in Michaelis-Menten and dissociation constant of both substrate and products. Finally, the recycled enzyme showed good retention of activity up to 6 cycles in presence of ultrasound, which further enhanced with water addition to reaction mixture.