2-Acetyl-1-pyrroline (2-AP) was identified as an important aroma compound of aromatic vegetable soybean. The level of 2-AP in 6 aromatic vegetable soybean lines was found to be positively correlated with popcorn-like aroma score. Comparison between aromatic and nonaromatic vegetable soybeans found that aromatic vegetable soybean contains higher concentration of methylglyoxal (MG) and Delta(1)-pyrroline-5-carboxylate (P5C) than a nonaromatic one. For MG formation-related genes, GapC was down-regulated and TPI was up-regulated in aromatic cultivar (Aromatic 7) as compared to nonaromatic control, which may contribute to the increase of MG level. Based on the data presented, a formation mechanism for 2-AP via interaction between MG and P5C in aromatic vegetable soybean was proposed.