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Cleome viscosa L. (Family: Capparaceae) commonly known as Tickweed or wild mustard and Tribulus terrestris L. (Family: Zygophyllaceae) commonly known as Gokhru, growing wildly in the desert areas in the monsoon and post monsoon season, are of great medicinal importance. Comparative larvicidal efficacy of the extracts from seeds of C. viscose and fruits and leaves oft terrestris was evaluated against 3rd or early 4th stage larvae of Anopheles stephensi (Liston), Aedes aegypti (Linnaeus) and Culex guinguefasciatus (Say) in different organic solvents. 24 and 48hr LC50 and LC90. values along with their 95% fiducial limits, regression equation, chi-square (chi(2))/ heterogeneity of the response was determined by log probit regression analysis. The 24hr LC50 values as determined for seeds of C. viscose were 144.1, 99.5 and 127.1 (methanol); 106.3, 138.9 and 118.5 (acetone) and 166.4, 162.5 and 301.9 mg l(-1) (petroleum ether extracts) for all the three mosquito species respectively showing that methanol and acetone extracts were a little bit more effective than the petroleum ether extracts. Experiments were carried out with fruits and leaves of T terrestris with all the solvents and mosquito species. The 24hr LC50 values, as determined for fruits oft terrestris were 70.8,103.4 and 268.2 (methanol); 74.0,120.5 and 132.0 (acetone) and 73.8, 113.5 and 137.4 mg r (petroleum ether extracts) while the 24hr LC50 values for leaves were 124.3, 196.8 and 246.5 (methanol); 163.4, 196.9 and 224.3 (acetone) and 135.8,176.8 and 185.9 mg l(-1) (petroleum ether extracts) for all the three mosquito species respectively. The results clearly indicate that fruit extracts of T terrestris were more effective as compared to leaves extracts in the three solvents tested. Larvae of An. stephensi were found more sensitive to both fruit and leaves extracts oft terrestris followed by larvae of Ae. aegypti and Cx. guinguefasciatus. Extracts from the seeds of C. viscose were found less effective as compared to the fruit extracts of T terrestris indicating that active larvicidal principle may be present in the fruits of this plant species. The study would be of great importance while formulating the control strategy, for vectors of malaria, dengue and lymphatic filariasis, based on alternative plant based insecticides in this semi-arid region.