The process of parental care can be complex, and it is rarely exhibited by reptiles. How predators influence the timing of parental care is still ambiguous in terrestrial vertebrates. In this study, we demonstrate that female skinks of Mabuya longicaudata adjusted to an experimental manipulation of interspecific intruders which were placed into skink nests. When the intrusion frequency of the reptile-egg eating snake, Oligodon formosanus, increased, the time spent on maternal care by M. longicaudata was significantly extended. In contrast, female M. longicaudata recognized two sympatric lizards (Sphenomorphus incognitus and Japalura swinhonis) which do not prey upon eggs or adults of M. longicaudata and did not attack those species; consequently, the time spent on egg-guarding did not significantly differ from the control treatment with intrusion by S. incognitus or J. swinhonis. Mabuya longicaudata also recognized the predatory snake, Elaphe carinata, and when that species entered a skink nest, the skink escaped and never returned. These results emphasize that the time spent on parental care is probably influenced by predators, and the duration of this behavior is dependent on the maternal defensive capability. As egg guarding is the most basic and primitive form of parental care, the current study provides evidence possibly leading to insights into the origin of parental care from reptiles to birds and mammals.