A systematic study was carried out to investigate the effect of alkali treatment and nanoclay on thermomechanical properties of jute fabric reinforced polyester composites (JPC) fabricated by the vacuum-assisted resin transfer molding (VARTM) process. Using mechanical mixing and sonication process, 1% and 2% by weight montmorillonite K10 nanoclay were dispersed into B-440 premium polyester resin to fabricate jute fabric reinforced polyester nanocomposites. The average fiber volume was determined to be around 40% and void fraction was reduced due to the surface treatment as well as nanoclay infusion in these biocomposites. Dynamic mechanical analysis (DMA) revealed enhancement of dynamic elastic/plastic responses and glass transition temperature (Tg) in treated jute polyester composites (TJPC) and nanoclay infused TJPC compared with those of untreated jute polyester composites (UTJPC). Alkali treatment and nanoclay infusion also resulted in enhancement of mechanical properties of JPC. The maximum flexural, compression, and interlaminar shear strength (ILSS) properties were found in the 1 wt % nanoclay infused TJPC. Fourier transform-infrared spectroscopy (FT-IR) revealed strong interaction between the organoclay and polyester that resulted in enhanced thermomechanical properties in the composites. Lower water absorption was also observed due to surface treatment and nanoclay infusion in the TJPC. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013