Recombinant form of β-galactosidase originated from Bacillus stearothermophilus, was immobilized on a chito- san matrix using tris (hydroxymethyl) phosphine (THP) and glutaraldehyde to hydrolyze lactose of milk. As a result, THP-immobilized recombinant β-galactosidase had high thermostability and showed great advantage for potential industrial use to produce lactose-hydrolyzed milk (Chen et al. 2009).