Acylase (EC 3.5.1.14) was immobilized on porous silica beads by cross linking with glutaraldehyde. The factors affecting the activity of the immobilized acylase, such as pH of the immobilization reaction, concentration of glutaraldehyde and amount of acylase were studied. We also studied the thermal properties of immobilized acylase. Thermal activation of this immobilized acylase was found at a temperature range of 50-90 o C. The durability of the immobilized acylase on heating was greatly improved. Even after incubation at 70 o C for 6 h, the activity of immobilized acylase was higher than that of the unincubated one.