Rat brain arylsulfatase A monomer was immobilized to CNBr-activated Sepharose 4B. The coupling of the enzyme could be accomplished up to the degree of 99%. The general properties of the immobilized arylsulfatase A were compared with those of the soluble enzyme. The enzymatic activity of the enzyme was conserved well by immobilization and the catalytic properties of the immobilized enzyme were similar to the soluble one except the increased Km value and the improvement of stabilities toward heat and pH. Thus the covalent coupling of the enzyme to Sepharose 4B did not affect vitally the functional groups of the active site of the enzyme. The two-pH optima profile of the immobilized enzyme imply that the multiple pH optima of the arylsulfatase A could not be explained solely by the monomer-dimer association.