Raman spectroscopy is a promising optical technique for blood diagnosis. This study assessed the diagnostic potential of Raman spectroscopy of serum by evaluating its ability to distinguish colon cancer patients and normal people. Raman spectroscopy of serum taken from normal people, colon cancer patients, and colon cancer patients after operation was collected by using an Ar-ion Raman spectroscopy system. Three parameters - Δλ, α, β - were used for the comparison among different groups. Thirty-five colon cancer patients were tested before and after operation, 22 normal people were measured as controls. The results show that Raman spectroscopy differentiated colon cancer from colon cancer after operation, and the controls.