The study aimed to determine the content of Low Molecular Weight Carbohydrate (LMWC), prebiotic, and prebiotic activity of thirteen food plants commonly consumed in Thailand. The prebiotics (inulin and fructooligosaccharide (FOS)) and LMWC content (glucose, maltose, sucrose, isomaltose, maltotriose, and maltotetraose) were determined using High Performance Liquid Chromatography (HPLC). Prebiotic activity of plant extracts (including LMWC and prebiotics) obtained from potential food plants was evaluated through cell density of Lactobacillus acidophilus grown on the extracts, commercial inulin, FOS, and glucose relative to that of Escherichia coli grown on similar media cultures. The results indicated that garlic contained significantly highest of inulin with the amount of 41.72% dry weight followed by shallot (33.22 %), and onion (27.17 %) whereas only small amount of inulin was detected in sweet potato, white radish, cassava, and yam bean (0.42-2.14%). There were no inulin and FOS found in rice. In the study on LMWC content, shallot contained the highest concentration of sucrose (11.42%) and glucose (2.91%) followed by onion. There were no maltose, isomaltose, maltotriose, and maltotetraose found in the bulbs and root/tuber crops studied, whilst the significant concentrations were observed in the germinated rice. For the study on prebiotic activity, Lactobacillus acidophilus grown on the extracts from onion, shallot, and garlic indicated the highest prebiotic activity scores comparable to that of commercial inulin while the prebiotic activity score of germinated rice were lowest and close to zero (0.17 and 0.23 in germinated non waxy and waxy rice, respectively). © Maxwell Scientific Organization, 2011.