Abstract: As a broad spectrum systemic organophosphorus pesticide (OPs), monocrotophos (MCP) is a potent neurotoxicant, which could result in neurotoxicity to non-target organisms. Behavioral toxicity is the main form of expression in neurotoxicity. The effects of MCP on the behaviors of a non-target organism, Caenorhabditis elegans, were studied using locomotion, learning, foraging behavior and acetylcholinesterase (AChE) activity as the endpoints. The results showed that after exposure to MCP (0.5,5.0 and 50.0 mg/L), there was a highly significant decrease in both head thrashes and body bends in all treated groups. The treatment of MCP also reduced the activity of forward turns, which was significant for 0.5 mg/L MCP and highly significant for 5.0 and 50.0 mg/L MCP. Meanwhile, the treatment of 5.0 or 50.0 mg/L MCP significantly enhanced the chemotaxis towards NaCl. Moreover, compared with the control groups of 2,4, 6,8 and 24 h, the attainment levels of C. elegans treated with 50.0 mg/L MCP were significantly decreased at 2,4, 6, and 8 h and extremely decreased at 24 h. In addition, the AChE activity of C. elegans significantly decreased in all treated groups in a dose-dependent manner. MCP caused obvious, severe defects of locomotion, learning and foraging behaviors in C. elegans, and there was a positive correlation between the inhibition of AChE activity and the effect of MCP on locomotion behavior, and a negative correlation between the inhibition of AChE activity and the effect of MCP on learning behavior.