Abstract: The histopathological changes induced by Sumithion® NP 25/2.5 EC, a newly formulated organophosphorous insecticide used in dengue fever vector control in Jeddah, Saudi Arabia, on rats testis were investigated. In addition to the control group, four experimental groups of male Wistar rats were daily injected intraperitoneally with two doses of Sumithion® NP 25/2.5 EC (1/10 and 1/4 the LD50; 80 and 200 mg kg-1 of body weight, respectively) for two and four weeks. Histological examination revealed significant alterations in the testis of all treated groups including: Focal mild testicular damages, blood hemorrhage and vascular congestion, hypospermatogenesis, dilatation and tubular deformity, cellular vacuolated degeneration (necrosis), aspermatogenesis and tubular destruction and atrophy. The observed pathological changes were dose and time dependent. The testicular toxicity of Sumithion® NP 25/2.5 EC was proven and alternative harmless control strategies should be applied.