The direct oxygenation of s-trans dienes, silyl dienol ethers (SDEs) 2, by triphenyl phosphite ozonide (TPPO) has been examined in detail. The regioselective oxygenation was found to give hydroperoxide 3, alcohol 4, ketone 5, dimer 6, and peroxy phosphate 7 with concomitant formation of triphenyl phosphate 8 and diphenyl trimethylsilyl phosphate 10. The formation of peroxy phosphate 7 was found for the first time in TPPO oxygenation reactions. The low temperature (31)P and (1)H NMR spectroscopic analyses proved the direct reaction of SDEs with TPPO without generation of singlet oxygen. The formation of the oxygenated products 3-7 is reasonably explained by the intervention of the zwitterion ZI, which can be formed by the nucleophilic attack of SDE to the central oxygen of the ozonide. The regioselective attack of SDE to the central oxygen of the ozonide was supported by the quantum chemical calculation (B3LYP/6-31G).