A divacant, lacunary, Keggin-type silicotungstate, [ホウ-SiW10O34(H2O)2]4-, exhibits high catalytic performance for the epoxidn. of various nonconjugated dienes using hydrogen peroxide under mild conditions, high regioselectivity to the more accessible double bonds, and high efficiency of hydrogen peroxide utilization. The high regioselectivity for the [ホウ-SiW10O34(H2O)2]4--catalyzed epoxidn. would be caused by the steric hindrance of the active site. [on SciFinder(R)]