Island mammals often display remarkable evolutionary changes in size and morphology.The aim of this study was to test the hypothesis that island mammals evolved at faster rates than their mainland congeners,and the evolution is faster on the smallest islands.In the study,we analyzed the morphological variations of ricefield rat (Rattus losea) populations from eight islands (areas ranging from 0.14 km2 to 93.66 km2) and of differing distance (isolation) from the mainland in Zhoushan Archipelago,China.The mean body mass of the ricefield rats was correlated negatively with island area,that is,the rats on small islands had a larger body mass.The mean body length,mean tail length,and mean ear length were also correlated negatively with island area.We also analyzed the relationship between the morphological parameters and the island isolation (the distance to the mainland) ,and found the mean tail length was negatively correlated with island isolation,but other parameters showed no significant correlation.Our study was consistent with the hypothesis that the morphological characteristics of island mammals evolve at faster rates in the smaller and more isolated islands.Future studies will explore the molecular genetics of these populations to determine whether our conclusions based on morphological variations hold true.