Poly (1,3-dioxepane) [PDOP] triol was prepared by cationic ring-opening polymerization with [C2H5C(CH2OCH2CH2CO+ClO4-)(3)], trioxocarbenium perchlorate, as an initiator. The structures of the PDOP triols obtained were verified by H-1-NMR, FTIR, and GPC results. Initiation, propagation, and termination mechanisms were discussed based on the structural analysis of the polyacetal polyols. The results of GPC, NMR, and IR measurements showed that the PDOP triols obtained had similar branch chain lengths. Number-average molecular weights were determined by vapor pressure osmometry (VPO), end group titration and H-1-NMR.