The chemical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity changes of ginsenoside $Rb_1$-glycine and ginsenoside $Rg_1$-glycine mixtures by Maillard reaction were investigated to identify the role of Maillard reaction in the increased antioxidant activity of ginseng by heat-processing. The DPPH radical scavenging activity of $Rg_1$-glycine mixture was more strongly increased by heat-processing than that of $Rb_1$-glycine mixture. From the analyses of ginsenosides, $Rb_1$ was gradually changed into 20(S)-$Rg_3$, 20(R)-$Rg_3$, $Rk_1$ and $Rg_5$ by heat-processing. $Rg_1$ was gradually changed into 20(S)-$Rh_1$, 20(R)-$Rh_1$, $Rk_3$ and $Rh_4$ by heat-processing. However, the generation of these less-polar ginsenosides was not related to the increased DPPH radical scavenging activity of $Rb_1$-glycine and $Rg_1$-glycine mixtures because their DPPH radical scavenging activities were already significantly increased when dried at $50^{circ}C$, which temperature induce no structural changes of ginsenosides. In the comparison of browning compound levels of $Rg_1$-glycine and $Rb_1$-glycine mixtures, the extents of Maillard reaction were positively correlated with their increased free radical scavenging activities. Based on the chemical and DPPH radical scavenging activity changes of $Rg_1$-glycine and $Rb_1$-glycine mixtures by heat-processing, we clearly identified that the increased free radical scavenging activity of ginsenoside is mediated by the Maillard reaction between sugar moiety of ginsenoside and amino acid.