The hydrophilic/hydrophobic organoclays with varying quaternary ammonium substituents (qas) were successfully synthesized and used as filler in unsaturated polyester (upe) resin-organoclay nanocomposites to enhance mechanical properties. the organoclay-bqasmmt18 (octadecyldimethylbenzylammonium bromide modified montmorillonite) with only 3 wt% in the upe enhanced tensile strength, tensile modulus, flexural strength and elongation at break by the order of 4.6, 2.4, 2 and 2.4, respectively compared to the pristine upe. the tensile strength and hardness of the upe-organoclay nanocomposites were increased with increase in organoclay content in the nanocomposites. however, the tensile and flexural strength decreased with increased loading of bqasmmt18 from 3% to 5 wt% due to less dispersibility of organoclay in nanocomposites. moreover, dispersibility of hydrophobic organoclays in upe nanocomposite is higher with respect of hydrophilic and pristine clay.