An $alpha$-D-galactosidase ($alpha$-D-galactoside galactohydrolase, EC 3. 2. 1. 22) from earthworm was purified by affinity chromatography using N-$varepsilon$-aminocaproyl-$alpha$-D-galactopyranosylamine coupled to sepharose and its properties were examined. The specific activity of the purified enzyme, tested with p-nitrophenyl-$alpha$-D-galactopyranoside as substrate, was 314 units/mg protein, representing an 122-fold purification of the original crude extract. The final preparation obtained from by Sephadex G-25 chromatography showed a single band on SDS-polyacrylamide gel electrophoresis. The molecular weight was determined to be 48,000 by SDS-polyacrylamide gel electrophoresis. The purified galactosidase was showed maximum activity at pH 4.5 and 4$0^{circ}C$, and was stable in the pH and temperature ranges from 4.0 to 5.5 and 30 to 5$0^{circ}C$, respectively. The enzyme activity was inhibited by Zn2+, Hg2+ and Co2+. When the purified $alpha$-galactosidase treated to guar gum for 6 hour, gel-promoting property was increased. It was clear that enzymatic elimination of galactose from guar gum by purified $alpha$-galactosidase would lead to a significant increase in gelation ability.