Abstract: Diethyl phthalate (DEP) is a typical plasticizer that has been widely detected in the environment. DEP possesses potential neurological and reproductive toxicities, which can affect the development motion behavior as well as certain biochemical parameters of organisms. The present study was designed to evaluate the eco-toxicity of DEP under different exposure scenarios (24 h, 72 h and 10 d) at environmentally relevant concentrations (0, 0.0002, 0.002, 0.02, 0.2, 2 mg/L) on Caenorhabditis elegans, a typical model animal. To this end, the body length/width, head thrashing frequency, and biochemical indicators of C. elegans were applied as test endpoints to evaluate the ecotoxicological effects of DEP. The results revealed that under 24 h exposure scenario, compared to the control group, DEP exhibited no distinct effect on the development of C. elegans at all exposure levels (P>0.05). In the case of 72 h exposure, DEP was found to inhibit the development of C. elegans compared with the control group. Specifically, the body length declined by 3.21% (P < 0.05) at a DEP level of 2 mg/L. Under 0.0002 mg/L DEP exposure, the body width was found to increase. Head thrashing frequency displayed stimulating effect when exposed to low DEP levels (< 0.2 mg/L). When it was 0.0002 mg/L, it increased by 5.52% (P < 0.01). In addition, the physiological endpoints, including body length, body width and head thrashing frequency, decreased significantly by comparison with the control group at all exposure levels after 10 d exposure. Moreover, the levels of reactive oxygen species, lipofuscin and apoptosis increased significantly at 2 mg/L. The results revealed that DEP exposure exhibited different toxicological effects on C. elegans, depending on the concentration and exposure scenarios.