The present study aimed to identify the mosquito vectors distributed throughout AL-Ahsaa district situated in the eastern region of Saudi Arabia. Mosquito larvae were collected seasonally for one year (October 2009 to September 2010) from different breeding sites in seven rural areas utilizing long aquatic nets. Salinity and pH of these breeding sites were also measured seasonally. The survey revealed the presence of five mosquito species, Aedes caspius Pallas (Diptera: Culicidae), Anopheles multicolor Cambouliu, Culex perexiguus Theobald, Culex pipiens L., and Culex pusillus Macquart, representing three genera; four of them (Ae. caspius, An. multicolor, Cx. perexiguus, and Cx. pipiens) are important vectors of diseases. Ae. caspius is the most common vector followed by Cx. pipiens and then Cx. perexiguus. Mosquitoes in AL-Ahsaa are prevalent in both winter and spring seasons, rarely encountered in summer, and are found in moderation during the autumn months. These results are compared with results of other regions in the Kingdom of Saudi Arabia.