For continuous production of galactooligosaccharides(GOS), β-galactosidase with high transgalactosylation activity from Bacillus sp. A 4442 was immobilized onto Diaion^(TM) HPA 75(styrene-divinylbenzene resin). The parameters influencing enzyme immobilization were scrutinized in order to maximize immobilization yield while minimizing enzyme inactivation. The optimum conditions turned out to be: Tris buffer concentration 30 mM, pH 8.0, contact time at room temperature 3 hr, and enzyme loading 25 ㎎ protein/ g resin. Both the thermal stability and the operational stability of immobilized enzyme were markedly enchanced by the treatment with 0.5% glutaraldehyde as a cross-linker. Under the experimental conditions established, the yield of β-galactosidase immobilization was 40% or more and the activity of the immobilized enzyme ca. 200 U/g resin. When a packed-bed reactor was employed to continuously convert lactose to GOS, the specific production, which refers to as the amount of commercially valuable GOS produced by a unit amount of immobilized β-galactosidase, was found to be ca. 300 g GOS/g carrier.