Marine halophytes (mangroves and sea grasses) were collected from the Red Sea coast of Egypt and tested for their mosquitocid al activities. The toxicities of mangroves Avicennia marina & Rhizophora mucronata, and seagrasses Thalassodendron ciliatum, Halodule uninervis and Halophilia stipulacea were examined against lab. Strain of 3 rd instar larvae of Culex pipiens. Results showed that extracts of seeds and leaves of Avicennia marina were more effective than other parts of the same plant as well as of the leaves of Rhizophpra mucronata against 3 rd instar larvae of Culex pipiens mosquito. On the other hand, comparison of the tox icities of the three species of sea grasses showed that crude extract of Halodule uninervis was more active against 3 rd instar larvae of mosquito Cu pipiens than crude extracts of Thalassodendron Ciliatum and Halophilia stipulacea . In view of these results, the purified active compounds from the most effective s amples found in our studies could be effective in killing mosquito larvae or repellin g adult female mosquitoes in an economic and safe manner.