Efficacy of fungal metabolites of Chrysosporium tropicum was evaluated against Culex quinquefasciatuslarvae in the laboratory to determine their larvicidal activity at 6 concentrations, with a mortality range of 10-95%. Efficacy of C. tropicum was analyzed by probit analysis procedures. The LC50 (concentration lethal to 50% ofthe population) values were 38.9, 63.7, 79.0, and 122.6 ul/ml for the 1st, 2nd, 3rd, and 4th instars, respectively. TheLC, values were 79.5, 95.6, 136.9, and 174.5 ul/ml against the lst-, 2nd-,3rd-, and 4th-stage larvai respectively.Lethal concentrations of fungal metabolites were significantly different among the 4 instars. Th-e lst-stage larvae weremost susceptible, whereas 4th instars were least susceptible to C. tropicum metabolites. The larvicidal potential of C.tropicum metabolites warrants fleld rials against various species of mosquitoes.