Wan-an Island is one of the most stable green sea turtle nesting sites in Taiwan. Each of the 11 beaches is characterized by various width, slope, grain size, and vegetation coverage. The digging success of the gravid female turtles on this island varies a great deal, and the average value is not high. Many investigations have demonstrated that the nest environment can influence the nest site distribution. The major environmental factors include: substratum compactness, vegetation coverage, grain size, and porewater content. Results of this study indicated that the substratum compactness is directly or indirectly influenced by other factors. This, in turn, would affect the digging success directly. The vegetation coverage can not only influence the substratum compactness but may act as an inducing factor for digging. As a result, the substratum compactness and vegetation coverage may be the most important environmental factors that influence the nest site distribution on Wan-an Island. The different combinations of various environmental factors might result in the high variation in digging success. Based on the result of this study, a hypothesis of nesting behavior of the green turtle on Wan-an Island is proposed. This is the first study ever that has demonstrated quantitatively the influence of beach characteristics on the nest site selection of the green sea turtles.