Peanut flour (PF) was fermented with four strains of lactic acid bacteria. The effect of fermentation on the antioxidant activities (α,α-diphenyl-β-picrylhydrazyl [DPPH] radical-scavenging activity, reducing power and Fe2+ chelating activity) and antioxidant compounds (phenolic acids and flavonoids) was investigated. Depending on the starter organisms used, lactic acid fermentation could increase the DPPH scavenging activity, reducing power and Fe2+ chelating activity of PF. The content of phenolic acids had a significant decrease (P < 0.05) after fermentation. Meanwhile, a significant bioconversion (P < 0.05) of rutin into quercetin was observed after fermentation. There was a good linear correlation between the EC50 value of DPPH scavenging activity (R2 = 0.8893, P < 0.05) or reducing power (R2 = 0.8893, P < 0.05) and the concentration of quercetin in PF. These results indicated that lactic acid fermentation might be a good process to obtain functional PF with high antioxidant activity.