Nonylphenol (NP), a representative endocrine disruptor, interferes with reproductive function in aquatic organisms and animals. Although many previous studies have focused on apoptotic cell death by NP, the fundamental mechanism of NP on apoptosis remains poorly understood. Here, we investigated the molecular mechanism on NP-induced apoptotic cell death in mouse TM4 Sertoli cells. To evaluate NP treatment on cell viability, formazan and lactate dehydrogenase (LDH) assays were performed. Results indicate that NP reduced cell viability and increased the release of LDH in dose- and time-dependent manners. The reduction of cell viability by NP treatment appeared to involve necrosis as well as apoptosis based on nuclear fragmentation, an increase in the sub G1 population, and the detection of poly(ADP ribose) polymerase and caspase-3 cleavage. Additionally, the anti-apoptotic protein Bcl-2 diminished, whereas the pro-apoptotic protein Bax increased in a time-dependent manner. Note that NP-induced apoptotic cell death was enhanced by the generation of reactive oxygen species (ROS) and activation of extracellular signal-regulated kinase (ERK) signaling. Pretreatment with N-acetylcysteine, an antioxidant, attenuated NP-induced apoptotic cell death. Moreover, NP caused a transient activation of the MAPK pathway. In particular, NP-induced cell death was significantly suppressed by U0126, a specific inhibitor of ERK. Taken together, our results suggest that NP induces apoptosis in mouse TM4 Sertoli cells via ROS generation and ERK activation.