There are four species of Onchidiidae in eastern coastal areas of China: Onchidium struma,Platevindex mortoni,Paraoncidium reevesii and Peronia verruculata.The last three species are new record ones in mainland China.Their ecological habits and external morphology were observed through field investigation and laboratory culture.The main indicators of biological characteristics were measured for statistical analysis.The reproductive system and digestive system of the four species were compared after anatomical observation of internal structure.The results indicate that the living habitats of these four species show a gradient which are respectively from a low tide zone to the high tide zone of the intertidal zone and then to supratidal zone.Their living habits and the ways of breathing are different because of different habitats.The differences on the externalmorphology of the four species are significant of which the color of feet and dorsal are different.Platevindex mortoni has no dorsal eyes with a gray black or grey white foot,and only Peronia verruculata has dendritic gills.The internal structure shows that Platevindex mortoni has no penis subsidiary gland while Paraoncidium reevesii has no penis traction muscles and as same as Peronia verruculata which has no anal glands.Foot length and foot width are found as typical indicators in the analysis of biological data of four species.The ratio of the length of pneumostome to posterior and anus to pneumostome is a significant observation indicator in comparison of genera and species.The special external structure and differences of the internal structure can be one of the main basis for classification in Onchidiidae.The comparative study of four species in eastern coastal areas of China has great significance to basic research in amending new type species and morphological re-description of Onchidiidae.