The aim of the present study is to investigate the effects of diallyl disulfide (DADS), an active compound of garlic, on certain serum biochemical and oxidative stress parameters in colon cancer induced by azoxymethane (AOM) in rats. The rats were divided into 5 groups: Control, AOM, DADS, AOM+DADS and corn oil. AOM-treated groups received 15 mg/kg sc AOM injections (twice at one-week intervals), while DADS-treated groups received 50 mg/kg DADS via gavage 5 days a week at the end of the 15th week. The corn oil group received 1 ml/kg corn oil via gavage 5 days a week (for 3 weeks) at the end of the 15th week of the study. Total protein and albumin (p<0.05) levels were higher in the DADS group than in the AOM group. ALP activity decreased in the DADS and AOM+DADS groups; whereas, ALT activity increased in the AOM group (p<0.05). Additionally, cholesterol and HDL levels lowered in the AOM and AOM+DADS groups (p<0.05). ROS concentration was significantly higher in the AOM group compared to the other groups (p<0.05), while GPx levels were low. Serum magnesium concentration was lower in the AOM+DADS group compared to the control group (p<0.05) and this decrease was accompanied by urea levels in both the AOM+DADS and DADS groups (p<0.05). Compared to the control group, iron levels were high in the DADS group, while chloride levels were high in the DADS, AOM+DADS and corn oil groups (p<0.05). In conclusion, the decreases in serum cholesterol and HDL levels, particularly in the AOM group, supported the notion that these parameters could be important cancer biomarkers in cancer cases. Furthermore, the changes in chloride and iron levels across groups were striking and it was concluded that many biochemical parameters could be identified as new biomarkers in colon cancer through investigation of the therapeutic efficacy of DADS.