This paper will examine the larvicidal properties of petroleum ether extracts of Jacquinia ruscifolia flower and Thuja orientalis strobili which have been combined to produce greater synergistic effects against Culex quinquefasciatus and Aedes albopictus mosquitoes. They were carried out in three conditions of concentration (50 ppm, 100 ppm, and 150 ppm plus in different proportions, 1:1, 1:2 and 2:1) and at different times (24, 48 and 72 hrs) of the extracts in various conditions (as extracts alone and in different mixtures). Findings were that there was high mortality of larvae with 100 percent death in Cx. quinquefasciatus with the 2: 1 mixture after 72 hours, and in Ae. Albopictus with the 1:2 mixture. The calculated synergy factors (SF) were always more than 1 in all treatments, which indicates a synergistic effect of the extracts, especially in Cx. quinquefasciatus in comparison with Ae. Albopictus. This study also brings out the possibility of using plant extracts as powerful larvicides in the control of the mosquitoes.