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The β-galactosidase A and B from Adsuki bean cotyledons were isolated by ammonium sulfate fractionation and DEAE-Sepharose FF ion exchange chromatography. The A form was further purified by CM-Sepharose FF ion exchange chromatography and Sephadex G-150 gel filtration. Purified β-galactosidase A showed one protein band on PAGE. It was also a single protein band on SDS-PAGE and its Mr was 3.3×104. Mr of A and B determined by gradient PAGE was the same as 1.4×105. It is suggested that β-galactosidase A comprised four identical subunits.The pI of β-galactosidase A and B estimated by isoelectric focusing PAGE were 7.6 and 4. 6 respectively. The apparent Km of A and B were 2. 08 mmol/L and 2. 45 mmol/L (ONPGal), 0. 75mmol/L and 1.24 mmol/L (PNPGal), 44 mmol/L and 25 mmol/L (lactose). Their activation energies were 43.9 kJ/mol and 34. 3 kJ/mol using ONPGal as substrate. Their optimum pH all were 4. 0. Their optimum temperatures were 50℃ and 55℃ respectively. Stability ranges of pH were pH 4. 0～6.0 and pH 3.5～5.0 separately. Galactose and lactose were reversibly competitive inhibitors. Ki for A were 6.21 mmol/L (galactose)and 329 mmol/L (lactcse),Ki for B were 3. 93mmol/L (galactose)and 169 mmol/L (lactose). Melibiose and raffinose were reversibly uncompetitive inhibitors against the enzymes. Metal ions and some chemical agents also showed inhibition against the enzymes.