Six manganese-containing heteropolytungstates, α-[(XO 4 )W 1 1 MnO 3 6 ] n - (XW 1 1 Mn; X = P, Si, B, and Zn), γ-[(SiO 4 )W 1 0 Mn I I I 2 O 3 6 H 6 ] 4 - (SiW 1 0 Mn 2 ), and [Mn I I 4 (H 2 O) 2 (PW 9 O 3 4 ) 2 ] 1 0 - (P 2 W 1 8 Mn 4 ) have been compared as catalysts for the oxidation of cyclohexene and cis-stilbene by iodosylbenzene. The yield of epoxide and the cis/trans isomer ratio of stilbene epoxides are dependent upon the charge of the XW 1 1 Mn catalysts. In addition to the oxidation reactions, isomerization of cis-stilbene to trans-stilbene was observed when an oxidized derivative of P 2 W 1 8 Mn 4 was used as a catalyst. Stoichiometric oxidation of cyclohexene or cis-stilbene by high-oxidation-state manganese-substituted heteropolyanions was also examined. Product distributions from stoichiometric oxidation are different from those from the catalytic reactions for each heteropolyanion, suggesting that different reaction pathways may be involved in these two types of reactions.