Catalytic properties of the title heteropoly compound, K-0.5(NH4)(5.5)[MnMo9O32]. 6H(2)O, were studied in homogeneous phenol hydroxylation with 30% hydrogen peroxide as oxidant. The effects of the amount of the title compound and V2O5, temperature, time, solvent and phenol/H2O2 molar ratio on catalytic activity were investigated. The experimental results indicated that the title heteropoly complex in the presence of V2O5 was an effective catalyst for the phenol hydroxylation with hydrogen peroxide. Under optimum conditions, the conversion of phenol was 45.04%; the yield and the selectivity of hydroquinone were 38.64% and 85.79%, respectively.