Heat-stable enterotoxin(ST) from enterotoxigenic E. coli eKT-53($ST^{+};LT^{-}$, transformant from isolate KM-7) that was produced in succinate salts medium. The culture supernatant(crude ST) was purifed by mulitpled steps and investigated some characterization of the ST. The heatstability of purified ST activity was completely lost by treating at $100^{circ}C$ for 30minutes. ST activity was lost by treatment at pH 1 and 12 conditions, while the activity was not reduced by treatment at pH 2~10, and then the ${alpha}-amylase$ and pepsin was not decreased activity but disulfide reducing agnets was lost the activity. The molecular weight of the purified ST was approximately 4,200, the isoelectric point was about 4.0.