Recombinant ${eta}$-galactosidase from Bifidobacterium longum LL04 was expressed in Escherichia coli and partially purified by ammonium sulphate precipitation and anion-exchange chromatography (Mono-Q). The optimum temperature and pH of the partially purified enzyme were $50^{circ}C$ and pH 7.0-8.0, respectively, when o-nitrophenyl-${eta}$-D-galactopyranoside was used as a substrate. The enzyme was stable over the pH range of 5.0-9.0, and was active at $40^{circ}C$ for more than 60 min at pH 7.0. The enzyme was significantly activated by $Na^+$ and $K^+$. Maximal activity was observed at the concentration of 10 mM for both $Na^+$ and $K^+$. The enzyme activity was strongly inhibited by most bivalent metal ions. The Km and Vmax on ONPG at 37 and $50^{circ}C$ were 0.72, 167.9, and 0.507 mM, 310.9 U/mL, respectively.