The purpose of this research was to investigate the composition of ginsenosides and to identify the chemical structures of ginsenosides generated from red ginseng by citric acid pre-treatment (RGC). The amount and the composition of ginsenosides in red ginseng (RG) and RGC were determined by high performance liquid chromatography (HPLC) analysis. The content of $Rg_3$, a well-known bioactive ginsenoside in RGC increased significantly (p<0.05) over 2 fold (0.411 mg/g) when compared with RG (0.186 mg/g). Moreover, the structures of 5 novel ginsenosides in RGC were investigated by liquid chromatography/mass spectrometry (LC/MS/MS) analysis. Three peaks were completely fragmentized from their mother ions to aglycones and suggested to be less polar ginsenosides $Rk_3/Rh_4$, $Rk_1$, and $Rg_5$. This study suggested that by processing red ginseng with citric acid it is possible to enhance the yield of both ginsenoside $Rg_3$ and less polar ginsenosides.