Background This study evaluated the effect of Jatropha curcas seed oil against adult American cockroach, Periplaneta americana, a mechanical disease vector, using three bioassay methods to determine the repellent activity, contact and fumigant toxicity. This involved the use of J. curcas oil solution (diluted with acetone (20%)) and J. curcas pure oil. For repellency test, concentrations 0.30, 0.60 and 0.90% v/v were used for the oil solution while 1.0 and 2.0 ml concentrations were used for the pure oil. All test groups were exposed for 15 min. Contact toxicity test involved the use of 0.30, 0.60, 0.90, 1.20 and 1.50% v/v concentrations for the oil solution while 1 and 2 ml concentrations were used for the pure oil. Exposure period for all test groups was 24–120 h. For the fumigant test, 0.15% v/v and 0.5 ml concentrations were used for the oil solution and pure oil groups respectively; exposure period for the test groups was 24–120 h. All test and the control groups had ten cockroaches (P. americana) per group with four replicates. Results Repellency was higher in test groups treated with pure J. curcas oil than in groups treated with the oil solution with repellency of 70–100% and 60–100% respectively after 15 min exposure period. For the contact test, a higher mortality rate was observed with the oil solution than the pure oil. Mortality was lower for 1 ml of pure oil with 20% at 24 h and 40% at 120 h than 2 ml of pure oil with 30% mortality at 24 h and 50% mortality at 120 h. A 100% mortality was recorded in the highest concentration (1.50% v/v) at 120 h. Fumigation test with 0.15% v/v of oil solution resulted in 20% mortality at 120 h while fumigation test with 0.5 ml of J. curcas pure oil resulted in 60% mortality at 120 h. Conclusion J. curcas seed oil possesses repellent and insecticidal properties against P. americana . Thus, the menace caused by this mechanical disease vector could be reduced using J. curcas seed oil.