Biobased polyurethane from soy oil derived polyol and diisocyanate on reinforcement with glass fibers enables to improve the mechanical properties of the base resin significantly. The effect of variation of glass fiber loading from 15, 30 and 50-wt% on the physico-mechanical properties of the resulting composites are evaluated and analyzed. The storage modulus of virgin biobased polyurethane gets a 14-fold increase on reinforcement with 50 wt% glass fibers. The results highlight a significant enhancement in strength and modulus of virgin biobased polyurethane by more than 260 and 480% respectively for a fiber content of 50-wt%. The original notch Izod impact strength of 26 J/m of the biobased polyurethane reaches 93, 200 and 448 J/m in composites with 15, 30 and 50 wt% of glass fibers. The environmental scanning microscopy (ESEM) analysis of the impact-fractured samples shows the efficiency of wetting and the distribution of glass fibers. Thermogravimetric analysis (TGA) shows the improved thermal stability of the biobased polyurethane on reinforcement with glass fiber. (C) 2004 Kluwer Academic Publishers.