Abstract: Objective To study the expression of homocysteine（Hcy） in serum of patients with common malignant tumor. Methods Fasting expression levels of Hcy in serum of 382 patients with established malignant tumor and in 190 healthy controls were measured with cycle enzyme methods. Results The expression levels of Hcy were significantly higher in patients with malignant tumor than in controls（（12.34±0.87）μmol/L-（19.76±1.85）μmol/L vs（9.22±0.37）μmol/L,P＜0.01）. Conclusion The expression level of Hcy in patients of different cancers increases,which needs to be further studied.