Essential oils being natural products, biodegradable and ecologically safe are emerging candidates as replacement of synthetic pesticides in pest management programme. In the present study, essential oils were isolated by hydrodistillating dried fruits of Cuminum cyminum (Apiaceae) and Piper nigrum (Piperaceae) and its repellant, fumigant toxicity and effect on acetylcholinesterase enzyme (AChE) activity was determined against rice weevil, Sitophilus oryzae. C. cyminum and P. nigrum essential oils showed significant (p<0.05) repellant activity and caused fumigant toxicity in S. oryzae adults with median lethal concentrations (LC50) 0.67 and 0.58 μL cm-3 air, respectively. Fumigation of S. oryzae adults with sublethal concentrations of C. cyminum and P. nigrum essential oils significantly (p<0.05) inhibited AChE activity. Reduction in AChE activity was 77.38 and 50.0 and 75.0 and 53.57% of the control after 24 h of fumigation with 40 and 80% of 24-h LC50 of C. cyminum and P. nigrum essential oils, respectively. In conclusion, these essential oils probably induce toxicity in insects by inhibiting AChE activity.