Entomological studies on the species composition, seasonal variation and infection rates ofrnAnopheles mosquitoes were conducted at four selected villages of Koka area, CentralrnEthiopia, between December 2006 and November 2007. Collection and identification ofrnlarvae of Anopheles from various breeding habitats during the study period indicated thatrnthere are three species, namely Anopheles gambiae s.l. (84.7%), An. pharoensis (14.4%) andrnAn. squamosus (0.9%). Similarly, a total of 8, 279 adult anophelines mosquitoes representingrnthree species were collected through indoor (7784) and outdoor (495) samplings. Overall, An.rngambiae s.l. was the predominant species, making 90.1% of all collections followed by An.rnpharoensis (9.6%). Both species were abundant after the short rainy season and remainedrnhigh through the wet season, and declined in the dry season. Peak indoor resting density wasrnobserved in May. The ratio of fed to half gravid and gravid combined for An. gambiae s.l. inrnindoor resting collection was 4.9:1, indicating high degree of exophily in the study area. Thisrnwas also supported by high number of half-gravid and gravid An. gambiae s.l. in outdoorrncollection than indoor. Similarly, high exophilic behavior (3.5:1) for An. pharoensis was alsornobserved.rnOf 662 An. gambiae s.l. and 246 An. pharoensis dissected from all collections; the averagernparous rate was 31.4% and 28.0%, respectively. None of the 208 parous An. gambiae s.l andrn69 parous An. pharoensis analyzed by ELISA to detect sporozoite antigen of P. falciparumrnand P. vivax were found infected. This seems to support the parasitological data during thernstudy period. Although no sporozoite infection rates was detected An. gambiae s.l.rn(presumably An. arabiensis) seems the principal vector of malaria in the area.