To know whether a short-term exposure to a commonly used insecticide induces subtle negative toxic effects, female western mosquitofish, Gam-busia affinis, were exposed to 0.1, 0.5, and 1 pub endosulfan for one week and subsequently examined for their olfactory and sexual attractiveness to conspecific males. A short-term exposure to endosulfan did not impair the physical conditions investigated in this study nor did it disrupt olfactory attractiveness of female mosquitofish. However, 1 ppb endosulfan significantly reduced sexual attractiveness of exposed females. Test males showed significantly less copulation attempts with the exposed females. Our results suggest that in the field, a short term exposure of endosulfan may disrupt mating processes in non-targeted aquatic organisms.