In order to investigate the chilling effect and consequently oxidative stress on anti-oxidant system of two rice cultivars a field experiment was conducted in Research Center of Agriculture and Natural Resource of Khouzestan in February and March 2011. The experiment was conducted in a split plot arrangement using a randomized complete block design with three replications. The main plot consisted of three sowing dates, including19th and 28th of February and 10th of March and two rice cultivars (Champa and Dollar) were randomized in sub-plots. Results showed that low temperature decreased the activity of anti-oxidative enzymes including Peroxidase (POX), Catalase (CAT) and Ascorbate peroxidase (APX) of leaf and root of both cultivars significantly. The lowest activity was in Dollar variety. Amount of Malondialdehyde (MDA) increased significantly during chilling stress. The largest amount of MDA was in the leaves and root of Dollar cultivars (59.8 and 20.95 mM. grFW) in second sowing date. Protein content of leaf and root of two cultivars was decreased. Therefore, Champa cultivar due to effective anti-oxidant system and decreased of MDA content was more tolerant chilling and oxidative stress in comparison to Dollar cultivar.