Abstract: Objective: To investigate the clinical significance of serum cytoplasmic thymidine kinase-1( TK1) in the diagnosis of digestive system carcinoma. Methods: The serum levels of TK1 in 144 patients with digestive system carcinoma and 60 healthy people were detected by enhanced chemi-luminescence assay. The data were statistically analyzed. Results: The TK1 positive rates in the patients with digestive system carcinoma( 59. 0%) were significantly higher than that in healthy people( 11. 7%)( P 0. 01). The TK1 positive rates in adenocarcinoma( 72. 7%) and hepatocytic carcinoma( 68. 6%) were higher than that in squamous cell carcinoma( 20. 0%)( P 0. 05). The TK1 positive rates in gastric,hepatic,pancreatic and colonic carcinoma were higher than that in esophagal squamous cell carcinoma( P 0. 05). Conclusions: The TK1 positive rate is high in digestive system carcinoma,especially in the adenocarcinoma of stomach,colon and pancreas and hepatocytic carcinoma,which surgest that the serum TK1 level is specific to the digestive gland carcinoma. The high expression of serum TK1 has certain applicative value in the screening and diagnosis of gastrointestinal adenocarcinoma and hepatocytic carcinoma.