Three tern species, Roseate Tern (Sterna dougalli), Bridled Tern (Sterna anaethetus) and Crested Tern (Sterna bergii) co-bred at Baisha islet, east-north of Penghu, in the summer of 2006. Each species favored different kind of environment for nesting. All Crested Terns nested in the flat plane with vegetation; Roseate Terns in the cliff near the vegetation, and Bridled Tern primarily nested near the vertical rock or under a rocky roof. The Crested Tern had the highest nesting density, and Bridled Tern nested loosely. The hatching success of Roseate (75%) and Crested Tern (73%) were significantly higher than that of Bridled Tern (30%). Roseate and Crested Tern laid eggs synchronously and had apparently two wave of egg laying and the breeding performances between early- and late-laying period were quite different. The relationship between hatching success and nest-site characteristics of the three species was investigated. The results revealed that hatching success of Roseate Tern increased with the number of walls and neighbors. Early-laying nests (79%) and central nests (72%) were more successful than late (11%) and edge nests (45%) of Roseate Terns. The laying-period was also important factors affecting hatching success of Crested Tern. Overall, the low hatching success of the late-laying nests may be due to the change of environmental conditions and the losing advantage of group breeding in the late season. The low hatching success of Bridled Tern was considered owing to the asynchronous laying pattern, loosely built nesting and weak parental behaviors.