Abstract: Using a fast method to measure serum lipid-bond sialic acid (LSA) of the patiengs with en-docranial tumors diagnosed by computed Tomography,the results showed that the serum LSA quan-tity of malignant or metastatic tumor group (143士42mg/L, n=59) was significantly increased than those of benign tumor (97士30mg/L，n=33)，non-tumor lumps (93士16mg/L, n=6) and control (94士18mg/L, n=80);the LSA positive rate of the first group (76. 3 0 0 ) was higher than other groups (9.1%，0, 10. 0%)(P<0. 001)" It was demonstrated in 47 cases of malignant tumors that the quantities and positive rate of serum LSA was positively related to the malignant degree of the tumors and incomplete degree of their wraping membrane，but not to the sizes of the tumors. It is suggested that measuring serum LSA is valuable in diagnosis，differential diagnosis and predictive analysis before operation of endocranial malignant tumors.