Colon cancer (CC) is accepted as the third type of cancer that causes death in the world. Oxidative stress and low glutathione peroxidase (GPx) activity can cause CC. This study aims to show whether GPx and Oxidized (GSSG)/ reduced glutathione (GSH) levels, which are considered oxidative stress markers, are effective in the etiopathogenesis of CC. Erythrocyte isolation was performed in 3 ml blood sample taken from volunteers aged 18-75 years. Hemoglobin amounts were determined from the standard graph drawn by monitoring the conversion of methemoglobin to cyanmethemoglobin in the presence of cyanide at 540 nm. Glutathione peroxidase activity was determined by spectrophotometric monitoring of NADPH+H+ (reduced nicotinamide adenine dinucleotide phosphate) oxidation at a wavelength of 340 nm. The amounts of oxidized and reduced glutathione were determined by using the standard graph drawn by following the 412 nm wavelength of the formation of 2-nitro-5-thiobenzoic acid, which has a yellow color. GPx activity of individuals with CC is 5.64 ± 1.49 U/gHb, GSH concentration is 6.96 ± 1.45 nmol/gHb, and GSH/GSSG ratio is 1.04 ± 0.49, GPx activity of healthy individuals is 10.52 ± 2.22 U/gHb, GSH concentration 11.43 ± 1.90 nmol/gHb, and GSH/GSSG: 3.86 ± 1.30, that is, the values of the patient group were significantly lower than the control group. Current results suggest that GPx activity, GSH concentration and GSH/GSSG ratio can be used as CC markers in the diagnosis and monitoring of disease course, and that the decrease in these parameters may be associated with an increased risk of CC.