Objective  To verify differential expression of ASS1 in clear cell renal cell carcinoma (ccRCC), clarify it with the development of ccRCC.Methods  23 pairs of ccRCC tissue samples were collected. We used Real-time PCR and immunohistochemical methods to detect the expression levels of ASS1 mRNA and protein in ccRCC cancer tissues and adjacent normal tissues. The content of citrulline was detected by using human citrulline ELISA kit.Results  The expression levels of ASS1 mRNA and protein in ccRCC cancer tissues are significantly lower than in the adjacent normal tissues, ELISA results showed that the content of citrulline in ccRCC cancer tissues higher than in adjacent normal tissue.Conclusion The ASS1 expression are significantly decreased in cancer tissues of ccRCC, and the accumulation of citrulline is found in cancer tissues. These results have a certain academic significance in illustrating the molecular mechanism of the ccRCC development and provide a new way of thinking for ccRCC diagnosis and treatment.