A decrease of 27.89% in free formaldehyde content at a rate of 15% rate of UF resin and 1.0% tannin solution was obtained. The IB value of the MDF panel was a decrease of 12.04%, the MOR value was a decrease of 27.80%, and the MOE value was a decrease of 18.05%. These reductions in some mechanical properties of MDF panels in decreasing UF resin ratio. The minimum free formaldehyde content in MDF panels was determined by using 15% UF resin and 1.0% tannin solution.