Abstract: Objective To determine the association between serum cystatin C and tumors. Methods Serum samples were obtained from 273 patients with tumors and 185 healthy volunteers. Serum cystatin C was determined by particle-enhanced turbidimetric immunoassay (PETIA). Student t-test, covariance analysis and multiple linear regressions were performed to examine the differences in the levels of cystatin C between the two groups. Results The student t-test did not show significant statistical differences in the serum cystatin C levels between the two groups (P=0.075). However, such differences became statistically significant (P<0.01) after adjustment of age. The multiple liner regression demonstrated that healthy volunteers and men had higher levels of cystatin C than those with tumors and women. Cystatin C also increased with age and decreases with estimating glomerular filtration rate. Conclusion Cystatin C may be associated with the genesis and development of tumors.