Betaine aldehyde dehydrogenase (EC 1.2.1.8, BADH) was purified from soybean (Glycine max) axes by ammonium sulfate fractionation, acetone fractionation, Sephacryl S-300 and 5`-AMP Sepharose 4B chromatography. The molecular weight of the enzyme was estimated to be 120,000 daltons by a gel filtration while the SDS-PAGE analysis gave a single band at the molecular weight of 60,000 daltons. The isoelectric point determined by isoelectric focusing was 5.69. The optimal pH for the activity was 10.0 and the optimal temperature was 45℃. The K_m values for betaine aldehyde and NAD+ was 0.69 mM and 19 μM, respectively. It was found that all 50 μM Li^+, Na^+, and K^+ and 100 μM Fe^(2+) activated the dehydrogenase reaction of BADH as much as 265%, 148%, 127% and 144%, respectively. The enzyme was inhibited by polyamines such as spermidine, spermine, agmatine, putrescine and cadaverine.