Nonylphenol (NP) as an environment contaminant has been demonstrated to adversely affect male reproduction. The main objective of thisstudy was to evaluate NP-induced oxidative stress and toxicity in testicular Sertoli cells. Sertoli cells were exposed to 10-40 _M NP for 24 h.Cell death and growth inhibition were observed by flow cytometric analysis and 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide(MTT) assay, while fluorescein diacetate (FDA) and propidium iodide (PI) staining was used to examine the morphological changes following NPexposure. Subsequently, we found that short-term treatment (2 h) of NP caused intracellular accumulation of reactive oxygen species (ROS), whichwas evaluated by loading of 2_,7_-dichlorodihydrofluorescein diacetate (DCFH-DA) without visible morphological changes. Loss of mitochondrialmembrane potential (MMP) was detected following 12 and 24 h treatment of NP and assessment by Rhodamine 123 (Rh123) staining. In addition,incubation with NP for 12 h also increased lipid peroxidation of Sertoli cells. These results indicated that low micromolar concentrations of NPinduce an adverse oxidative stress in rat Sertoli cells.