The enzyme urease (urea hydrolase.EC:3.5.1.5) cleavages urea to ammonium and carbon di-oxide. Immobilization of enzyme is mostly used in technology nowadays. For example: immobilized urease is used for detoxification and decreasing of blood urea. There are different types of matrix (nylon, polyacrylamide, DEAE cellulose, sepharose) which are used in immobilization of enzymes. There are different methods for immobilization of enzymes but adsorption, cross-linking and entrapment are more commonplace. In this study, the urease enzyme is immobilized on the new (Hydroxy apatite-gelatin) hybrid matrix by adsorption. The optimal pH and temperature for enzyme activity for both free and immobilized enzyme were studied. The enzymes were linking by hydrophobic forces and salt-bridges. The urease assay was done using nessler method in which produced ammonium from enzyme reaction makes yellow color complex which has adsorption at 480nm. The urea concentration was between 3-20mM. The enzyme activity was determined in the 50-75 temperature range and pH of 6-10. Optimum conditions for free enzyme is 67 !\"#$%\"&\'()*+\"#$%\" this is about 70 !\"#$%\"&H=8.7 for immobilized enzyme. It is illuminated that the immobilization of enzyme causes increasing of optimal temperature up to 3 units (67 to 70) and increasing optimal pH from 8.2 to 8.7.

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