Insecticide resistant strains of mosquitoes is considered as a main problem in controlling malaria and dengue diseases. In the present study, a fenitrothion resistant strain (FEN-R-strain) of Culex pipiens larvae in Assiut University, Assiut Egypt, proved to have a high level of cross-resistance against the organophosphate insecticides. Cross-resistance to malathion (RR₅₀ = 634.86-fold) was higher than that of fenitrothion (RR₅₀ = 426.70-fold), whereas the cross-resistance to diazinon (RR₅₀ = 97.86-fold) was lower than that of fenitrothion. RR₅₀ on the other hand, the resistant strain had low level of cross-resistance toward chlorpyrifos (RR₅₀ were 31.8-fold) as compared with the other tested organophosphates. The results revealed that larvae of FEN-R-strain displayed slightly high cross-resistance to the pyrethroid insecticidedeltamthrin (RR₅₀ = 22.32-fold), moderate cross-resistance tocypermthrin (RR₅₀ = 16.90-fold) andpermethrin (RR₅₀ = 12.64-fold) and lless cross-resistance level was to fenvalerate (RR₅₀ = 1.67-fold). Larvae of FEN-R-strain displayed high cross-resistance to the carbamate insecticidepropoxure (RR₅₀ = 10.18-fold), low cross-resistance or tolerance tocarbaryl (RR₅₀ = 4.13-fold) and very low cross-resistance or tolerance to methomyl (RR₅₀ = 1.96-fold).Data also indicated that larvae of the FEN-R-strain of Culex pipiens displayed slight cross-resistance to the bioinsecticidespinosad (RR₅₀ = 250.53-fold) and low cross-resistance or tolerance to avermectin (RR₅₀ = 8.52-fold). Larvae of FEN-R-strain showed moderate cross-resistance or tolerance to the insect growth inhibitor insecticidepyriproxyfen (RR₅₀ = 10.30-fold). The variability in cross-resistance values in larvae of FEN-R-strain of Cx. pipiens to different conventional insecticides seem to indicate the absence of single mechanism controlling resistance among and within the insecticides classes (organophosphate, pyrethroide, carbamate, bioinsecticide and IGR insecticides). This pattern suggests multiple mechanisms of resistance, i.e. metabolic resistance and insensitive target site.