β-Galactosidases (β-Gal, EC 3.2.1.23) catalyze the cleavage of terminal non-reducing β-D-galactose residues or transglycosylation reactions yielding galacto-oligosaccharides. In this study, we present the isolation and characterization of a β-galactosidase from Arion lusitanicus, and based on this, the cloning and expression of a putative β-galactosidase from Arion vulgaris (A0A0B7AQJ9) in Sf9 cells. The entire gene codes for a protein consisting of 661 amino acids, comprising a putative signal peptide and an active domain. Specificity studies show exo- and endo-cleavage activity for galactose β1,4-linkages. Both enzymes, the recombinant from A. vulgaris and the native from A. lusitanicus, display similar biochemical parameters. Both β-galactosidases are most active in acidic environments ranging from pH 3.5 to 4.5, and do not depend on metal ions. The ideal reaction temperature is 50 °C. Long-term storage is possible at up to +4 °C for the A. vulgaris enzyme, and at up to +20 °C for the A. lusitanicus enzyme. This is the first report of the expression and characterization of a mollusk exoglycosidase.