BACKGROUND Ecological data are important in the vector control management of mosquitoes. There is scattered published information about the larval habitat characteristics and ecology of the genus Anopheles (Diptera: Culicidae) in Iran and most of available data is in relation to malaria vectors in southern Iran. METHODS This cross sectional investigation was carried out to study the mosquito fauna and ecology in Guilan Province, northern Iran, during April-December 2000. Larvae were collected using the standard dipping technique. Larval habitat characteristics were recorded according to water situation (clear or turbid), vegetation, substrate type, sunlight situation, habitat situation (transient or permanent, running or stagnant), habitat type (natural or artificial), and water temperature. RESULTS In total, 1547 third- and fourth-instar larvae of Anopheles from 90 habitats were collected and morphologically identified. Five species; Anopheles claviger, An.'hyrcanus', An. maculipennis s.l., An. plumbeus, and An. superpictus were identified and respectively comprised 6.3%, 22.4%, 54.4%, 13.0%, and 3.9% of the samples. The mean and range temperatures of the larval habitat water were 19.6°C (n=14) (16-25°C), 22.6°C (n=53) (12-33°C), 23.8°C (n=52) (10-33°C), 11.5°C (n=12) (9-21°C), and 20.4°C (n=7) (12-26°C), respectively. There was a significant difference in the mean water temperatures (11.5-23.5°C) of the larval habitats of different species (P=0.000). Most of the genus larvae were collected from natural habitats (86.9%) such as river bed pools (46.4%) and rain pools (33.1%) with transient (98.3%), stagnant (99.5%) and clear (95.3%) water, with vegetation (69.9%), mud (42.0%) or gravel (39.7%) substrate in full sunlight (69.6%) or shaded (22.7%) area. A checklist of the province mosquitoes including 30 species and seven genera has been provided. CONCLUSIONS The main larval habitats of the most abundant species, An.'hyrcanus' and An. maculipennis s.l., in Guilan Province are: river bed pools, rain pools, and rice fields.