Some metal ions play a cofactor role for the activity of tyrosinase enzyme and one of them is copper ion. In this study an amperometric biosensor was developed in order to investigate the effect of the copper ions on the activity of tyrosinase enzyme. In the construction of the biosensor tyrosinase enzyme was immobilized on a Clark-type dissolved oxygen probe which was covered with a oxygen sensitive teflon membrane, by using a chemical covalent immobilization method based on gelatine and bifunctional reagent, glutaraldehyde. The principle of the measurement was based on the determination of the differentiation of dissolved oxygen level in the enzymatic reaction catalyzed by tyrosinase in the absence and the presence of copper ions. Differences between the dissolved oxygen concentrations were related to copper ion concentration which was added in to the reaction medium. The biosensor response depends linearly on copper ion concentration between 2.5-20.0 mu M with a response time 1 min. The detection limit of the biosensor is 0.95 mu M.