The potential toxicity of five selected herbicides i.e. bispyribac-sodium, penoxsulam, haloxyfop-p-ethyl, pinoxaden, and tralkoxydim, and a pyrethriod insecticide deltamethrin was determined on the early 4th instar larvae (after 24, 48 and 72-h exposure) and pupae (after 24 and 48-h exposure) of Culex pipiens L. in the laboratory. As a result, deltamethrin was count as the most toxic compound on the early 4th instar larvae and pupae of Cx. pip- iens compared with all tested herbicides after exposure times. For the tested herbicides, pinoxaden was the most potent herbicide against both tested developmental stages fol- lowed by bispyribac-sodium and penoxsulam, which exhibited a moderate toxicity; while haloxyfop-p-ethyl and tralkoxydim were deemed to be the lowest toxic compounds among all tested pesticides after exposure times. In addition, the toxicity of all pesticides against larval and pupal stages of mosquito was increased gradually as exposure time increased especially after 72-h exposure for larvae and 48-h exposure for pupae. In conclusion, this is the first report on the side toxicity effects of haloxyfop-p-ethyl, tralkoxydim, penoxsulam and bispyribac-sodium on immature stages (larvae and pupae) of Cx. pipiens mosquitos in Egypt.