The effects of kefir fermentation were investigated on antioxidation activities (in vitro) and antioxidative stress (in vivo) for different Thai rice; Hawm Nil rice, Red Hawm rice and Khao Dawk Mali 105 rice. Methodology: Antioxidant activity (in vitro) was investigated using ferric reducing antioxidant power and 2, 2´-diphenyl-1-picrylhydrazyl assays. In addition, antioxidative stress (in vivo) was performed using colitis rat models to study nitric oxide (NO), lipid peroxidation (LPO) and superoxide dismutase (SOD) compared with rats treated with prednisolone and cow’s milk kefir. Results: Antioxidant activity of rice kefir powder from both assays had higher antioxidant activity than cow’s milk kefir powder. NO levels of colitis rats received Hawm Nil rice kefir powder (HNKP) was reduced when compared to phosphate buffered saline (PBS) group. Moreover, colitis rats received HNKP did not differ in NO levels from colitis rats that received prednisolone and non-colitis rats. The result of LPO product malondialdehyde (MDA) indicated that colitis rats treated with HNKP had reduced TBARS compared to PBS group, and did not differ in TBARS levels from rats that received prednisolone and non-colitis rats. Surprisingly, increase in SOD activity was observed in colitis rats that received HNKP compared to PBS, with similar results of increased SOD in rats that received prednisolone and cow’s milk kefir powder. Conclusion: Hawm Nil rice kefir may offer a protective effect for antioxidative stress resulting from chemical induction; it has potential as a supplementary food with high antioxidant activity and is regarded as safe for consumer health.