This study is a result of activities and research carried out during May–September, 2003. One breeder group of Whiskered Tern (Chlidonias hybridus) (930 pairs) in Zarrinkola Ab-bandan and two breeder group (1390 pairs) in Marzoonabad Ab- bandan were investigated. Floating nests were made on the Nymphae alba. Some of the important factors of nest selection on the basis of observations and measurements were nest size, water depth around the nest and nest distance from the nearest nest for determination of habitat suitability and their division to different categories.The maximum nest length, nest width and nest cup length in Zarrinkola Ab-bandan were 36.06±13.65, 34.53±12.89 and 10.32±1.57 cm, respectively. The maximum nest thickness of water level, nest cup depth and water depth in the first breeder group of marzoonabad Ab-bandan were 3.85±0.46, 1.75±0.31 and 186.33±7.06 cm, respectively. The maximum distance of neighbor nest in second breeder group in marzoonabad Ab-bandan was 4.16±3.32 m. There was no significant difference between breeding success with nest size (p=0.711, p=0.266, p=0.200), water depth (p= 0.070, p=0.777, p=0.103) and distance of neighbor nest (p=0.851, p=0.050, p=0.502) in Zarrinkola, first and second breeder group of Marzoonabad Ab-bandans, respectively.