Objective To investigate the effects of prolonged starvation on aminotransferases, phosphatases, proteinaes and proliferating cell nuclear antigens (PCNA) in planarians. Methods Automated biochemistry analyzer was employed to determine the enzymes activities of aminotransferases, non-denatured electrophoresis (G-PAGE) was used to analyze enzymes activities of phosphatases and proteinaes, the semi-quantitative RT-PCR was employed to investigate the expressed changes of PCNA mRNA. Results The activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) elevated apparently during starvation, 10-fold higher than that of the control level, but reduced to the normal level after re-fed; The activities of alkaline phosphatase (ALP) decreased during starvation, whereas the activities of acid phosphatase (ACP) increased apparently; In response to starvation, the activities of 140kD and 40kD proteinases increased drastically; However, no changes of the expression level of PCNA mRNA during starvation were observed, which indicated that starvation had little influences on this gene. Conclusion Prolonged starvation has greater effects on the physiology and biochemical metabolism of planarians, and the changes of enzyme activities reflecte the changes of energy metabolism of planarians in response to prolonged starvation. This findings provide a basis for further understanding the physiological mechanism that planarians are in adaptation to starvation.