Selenium in the form of sodium selenite (SSE) is an essential micronutrient which known to possess antioxidant and anticancer properties. This study emphasizes the role of selenium on oxidative stress in experimental rats with N-diethylnitrosamine (DEN) initiated and 2-acetylaminofluorene (2-AAF) promoted multistage hepatocellular carcinogenesis (HCC). Rats were divided randomly into six groups: negative control, positive control (DEN+2-AAF), preventive group (pre-SEE 4 weeks+DEN), preventive control (respective control for preventive group), therapeutic group (DEN+post-SSE 12 weeks) and therapeutic control (respective control for therapeutic group). SSE (4 mg L(-1)) was given to animals before initiation and during promotion phase of HCC. The levels of total protein (TP), conjugated diens (CD), malondialdehyde (MDA), fluorescent pigment (FP), antioxidant activity (AOA) and DNA damage were measured. Supplementation of SSE before the initiation phase of carcinogenicity significantly increased TP and AOA level (p < 0.05) while it decreased the levels of CD, MDA, DNA damage and FP (p < 0.05). Supplementation of SSE during the promotion phase of carcinogenicity significantly decreased the DNA damage and FP level (p < 0.05) and there were negative correlation between the level of AOA and with the level of FP and CD. Thus, supplementation of SSE reduced the adverse changes which occur in liver cancer. However, the chemoprevention effect of SSE was more pronounced when it was supplemented before initiation phase of cancer when compared to promotion phase.