Urease was immobilized with calcium alginate by entrapment method in the form of spherical beads and stored in Tris/acetate buffer (pH 7.3) at $4^{circ}C$. Urease immobilized at different concentration of alginate beads (3%, 4% and 5%) showed higher apparent $K_{m}$ values than the soluble urease. Furthermore, $K_{m}$ has been shown to be corelated with effective diffusion coefficient (De) at different concentration of alginate gel. The present study showed that diffusion and reaction contribute to control the overall rate.