Raman spectroscopy of tissues has been widely studied for the diagnosis of various cancers, but biofluids were seldom chosen as the analyte because of the low concentration. Herein, serum of 30 normal people, 46 colon cancer, and 44 rectum cancer patients were measured using Raman spectra and analyzed. The information of Raman peaks (intensity and width) and that of the fluorescence background (baseline function coefficients) were selected as parameters for statistical analysis. Principal component regression (PCR) and partial least square regression (PLSR) were used on the selected parameters separately to see the diagnosing performance of the parameters. PCR performed better than PLSR in our spectral data. Then linear discriminant analysis (LDA) was used on the principal components (PCs) of the two regression methods on the selected parameters, and the diagnostic accuracy were 88% and 83%. The conclusion is that the selected parameters can maintain the information of the original spectra well and Raman spectroscopy of serum has the potential for the diagnosis of colorectal cancer.