The aim of this master thesis was the purification and characterization of a -galactosidase from the Spanish slug (Arion lusitanicus). -galactosidase, which belongs to the family of exoglycosidases, cleaves -glycosidic bonds between galactose and other sugar residues. Bacterial -galactosidase e.g. from Escherichia coli is commonly used and established as a reporter gene in micro- and molecular biology. It has already been sequenced and extensively analyzed, while so far very little is known about mollusc -galactosidases. The protein was purified from Arion lusitanicus by homogenization and gradient ammonium sulphate precipitation followed by several chromatographic steps. First, the enzyme was purified by two subsequent hydrophobic interaction chromatographies, followed by a ConA-affinity and a size exclusion chromatography. Finally, the protein was isolated by a -galactose-specific affinity chromatography. The purified sample was analyzed be electrophoresis. Four bands were isolated and further analyzed by LC-ESI MS. However, none of them showed homology with known -galactosidase sequences. The optimum pH of -galactosidase from Arion lusitanicus was determined between pH=5.0 and pH=6.0, depending on the buffer system. The optimum temperature for enzyme activity was found to be 50 C. The presence or absence of cations does not affect enzyme activity, the only exception being Cu2+, which inhibits -galactosidase.