The aim of the present study was to determine the capacity of producing antioxidant agents of Lactobacillus rhamnosus PN04. The ethanol precipitated culture of L. rhamnosus PN04 was studied for reducing power and DPPH radical scavenging activity on both supernatant and a 90% ethanol extract. The reducing power was increased in the stationary phase and decreased at the death phase. At 10mg/ml, the absorbance of water-soluble exopolysaccharide (WSPES) solution at the stationary phase showed the highest value at 0.0355, compared to ascorbic acid standard at concentration 671 μg/ml. This results indicated that both the supernatant (115.3x10^6 cfu/ml) and 10 mg/ml WSPES (at stationary phase) were the most active antioxidant with the percent inhibition of 95.19 ± 0.062 and 52.86 ± 0.133 when compared with ascorbic acid at 30.04 μg/ml and 5.455 μg/ml, respectively. Consequently, L. rhamnosus PN04 may be a potential natural antioxidant.