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The problem of rendering a transfer function strictly positive real using reduced-order observer is studied in this paper. It is shown that the problem always has a solution that is parameterized by a stabilizing feedback gain K and a positive definite matrix PK satisfying certain Lyapunov matrix equation. In addition, the resultant positive real transfer function is explicitly obtained and has the property that its Hinfin norm can be made arbitrary small if K and PK are properly chosen. The results are illustrated with some examples.