A mosquito larval survey was carried out in the southwestern region of Saudi Arabia. Twelve mosquito species were identified: 4 Anopheline species; Anopheles arabinesis Theobald, Anopheles tenebrosus Donitz, Anopheles multicolor Combouliu, and  Anopheles sergenti  Theobald and 6 Culicine species; Culex pipiens Linnaeus; Culex tritaeniorhynchus; Culex lutzia; Culex sinaiticus; Culex quinquefascitus Say; Culex theileri Theobad as well as one Aedine species, Aedes caspius, and Culiseta subochrea. Culex pipiens is the most common culicine species in the southwestern region. The insecticidal activity of tested compounds (acetonic and ethanolic extracts of agricultural waste product, rice bran and plant,extract of Milkweed) was bioassay against the 3^rd instars of the Culex pipiens larvae in the laboratory. Therefore, the toxicity of the tested plant extracts based on LC₅₀ values could be arranged in an ascending order as follows: ethanolic extract of milkweed leaves < acetonic extract of milkweed leaves < acetonic extract of milkweed flower < acetonic extract of  rice bran < ethanolic extract of  rice bran < ethanolic extract of milkweed flower.              The SR of ethanolic extract of Rice bran with Triton x100 (1.64) was higher than other one.