Biological control potential of Metarhizium anisopliae and Paecilomyces species against Culex quinquefasciatus was evaluated. M. anisopliae and Paecilomyces spp was isolated from soil using soil suspension method with selective isolation media. Bioassay was made to determine their efficacy against 4th instar larvae of C. quinquefasciatus. Three different concentrations; 1x106, 1x107 and 1x108conidia/ml were made and tested. Results showed that, mortality increased as the period of exposure increased and also increased as the conidia concentration increased. The mortality recorded in lowest dose of 106 conidia/ml was 60% and 50% in M. anisopliae and Paecilomyces spp respectively, and again 80% and 70%mortality was recorded at dose of 107 conidia/ml. whereas highest dose level of 108conidia/ml caused high mortality of up to 90% and 80% respectively. The lethal concentration causing 50% mortality (LC50) of 4th instars larvae of C. quinquefasciatus was also varied according to concentration of spores and duration of exposure. The result showed that LC50 values of M. anisopliae isolate were 3.8×108, 2.5 x 106, 2.0 x 105 and 1.7x107conidia/ml after 24, 48, 72 and 96 Hours exposure respectively. Similarly, LC50 values Paecilomyces Spp isolate were 5.3×108, 3.8 x 107, 2.0 x 106 and 2.3 x 107conidia/ml after 24, 48, 72 and 96 Hours exposure respectively. the These results indicated that M. anisopliae and Paecilomyces Spp isolated is pathogenic to immature stage of C. quinquefasciatu and could be suggested for development as a biological control for mosquitos’ management.