The purpose of the study was to assess the level of serum malondialdehyde (MDA) concentration and its association with the stage and histopathologic sizes of colorectal cancer (CRC). One hundred and two patients having undergone surgical treatment of CRC between January 2014 and December 2015 were included in this cross-sectional study. The patients were divided into four groups (stage I-IV) according to the TNM classification. Control group included 30 subjects with no signs of malignancy and inflammatory diseases. In each patient, preoperative blood samples were obtained for determination of MDA concentration by ELISA immunoassay. Serum levels of MDA were progressively increased in patients with CRC, reaching the highest value in the fourth stage of CRC. Serum concentrations of MDA were significantly higher in pT4 group as compared with pT3 and pT2 groups of CRC patients (p<0.01). Significantly higher levels of MDA were found in the N1 and N2 groups of CRC patients as compared with N0 group, as well as in patients with metastatic disease as compared with those without metastasis (p<0.001). In conclusion, the progression of CRC is associated with a significant increase in serum MDA levels.