Selective cis-dihydroxylation of olefins with the aid of a triple catalytic system using H2O2 as the terminal oxidant has been developed. In this process Os(VI) is recycled to Os(VIII) by a coupled electron-transfer-mediator system based on N-methylmorpholine and a biomimetic flavin, leading to a mild and selective electron transfer. Aliphatic, aromatic, and functionalized olefins were successfully cis-dihydroxylated, employing the triple catalytic system. The present biomimetic catalytic system works well in asymmetric dihydroxylation and gave optically active diols in good isolated yields and high enantiomeric excesses (up to 99% ee).