This study was conducted to ascertain the allelopathic relationship between Tithonia diversifolia and some cucurbits C. sativus, C. colocynthis and C. lanatus. Seeds of the cucurbits were treated every 24 hours with 10ml of different concentrations (0% [control], 25%, 50% and 100%) prepared from 2.5g/ml stock solution of aqueous extracts of T. diversifolia. Two experiments (the Petri and micro plot experiments) were conducted concurrently and were both laid out in a completely randomized design with four replicates in the Green house of Centre for Ecological Studies, University of Port Harcout. Data were taken on Radicle length, Plumule length, Number of leaves (NOL), Plant Height (PH), Fresh weight and Dry weight for five weeks after plating / sowing for the test cucurbits. Results showed that, compared to the control, there were no significant (p≤0.05) difference in all the parameters investigated for the three cucurbits studied after treatment with different concentrations of T. diversifolia. Results from the analysis shows that for laboratory (Petri dish) experiment, T. diversifolia inhibited the plumule of C. calocynthis in 25% concentration at 5 days after plating; the radicle and plumule of C. lanatus in 50 and 100% concentrations at 5 and 7 days after plating (WAP). T. diversifolia showed no effect on the radicle and plumule length of C. sativus. For Green house (potted) experiment, it stimulated the growth of C. sativus and C. calocynthis in 50% at 5WAP and stimulated the growth of C. lanatus in 25% at 5WAP. Conclusively, there are possibiliites that T. diversifolia possess allelopathic effect on the growth and development of some cucubits.