Methanolic extracts of leaves and seeds from the chinaberry tree, Melia azedarach L. (Meliaceae) was tested against mature and immature mosquito vector Anopheles stephensi Liston (Diptera) under laboratory condition. The extract showed strong larvicidal, pupicidal, adulticidal, antiovipositional activity, repellency and biting deterency. The M. azedarach seed and leaf extracts were used to determine their effect on A. stephensi adults and their corresponding oviposition and consequent adult emergence in comparison with the control. The seed extracts showed high bioactivity at all doses, while the leaf extracts proved to be active, only in the higher dose. Results obtained from the laboratory experiment showed that the seed extracts suppressed the pupal and adult activity of A. stephensi even at low dose. In general, first and second instar larvae were more susceptible to both leaves and seed extracts. Clear dose-response relationships were established with the highest dose of 2% plant extract evoking 96% mortality. Entire development of A. stephensi was inhibited by M. azedarach treatment. Less expensive (less than 0.50 US dollars per 1 kg seed), naturally accruing bio-pesticide could be an alternative for chemical pesticides.