The mechanisms of ruthenium-catalyzed synthesis of pyrrole from C4-olefinated isoxazole were investigated by employing the density functional theory (DFT) calculations. Three main steps are included in this reaction: N−O cleavage, 1,5-cyclization, and H-transfer steps. The H-transfer is calculated to be the rate-determining step. The role of Cu(OAc)2 employed in this reaction is to supply HOAc molecule to facilitate the H-transfer step.