A new method for the synthesis of propylene oxide using nascent oxygen generated during the electrolysis of water has been proposed. Among the noble metal blacks tested, the most active and selective anode electrocatalyst was Pt black. The oxidation of propylene was initiated at an applied voltage across the cell higher than ca. 1.1 V (anode potential higher than 1.1 V vs NHE). The formations of propylene oxide and acetone were enhanced remarkably at > 1.1 V applied voltage. The maximum oxidation efficiency for the sum of the two products was 56% at an applied voltage of 1.5 V (anode potential 1.3 V vs NHE). The epoxidation at applied voltage higher than 1.5 V enhanced the formation of by-products, CO2 > acetic acid greater than or equal to propionic acid. The kinetic curves of each product suggest that propylene oxide and acetone are formed in parallel; neither acetone, nor CO2, nor acetic acid are formed from the propylene oxide produced. The method was more effective for epoxidations of 1-hexene and cis- and trans-2-hexenes, The product ratio in cis- and trans-2,3-epoxyhexanes observed for the epoxidations of the 2-hexenes indicated the retention of the cis-trans configuration of the starting 2-hexenes. The oxidations of cyclohexane and benzene by the same method were quite slow, giving CO2 as the main product. Thus, the active oxygen generated in this system was quite specific for epoxidation of olefins. The calcination of an inactive Pt black in air at ca. 673 K enhanced remarkably its electrocatalytic activity for epoxidation of olefins. XPS studies on various Pt black samples suggested that the PtO2 phase was responsible for the formation of the active oxygen. A tentative Langmuir-Hinshelwood-type reaction mechanism has been proposed to account for the epoxidation results.