The synthesis of well-defined poly(vinyl acetate)-b-polystyrene (PVAc-b-PSt) by combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization was described. Two difunctional compounds, S-(2-chloropionoxyethoxycarbonylmethyl) O-ethyl xanthate (2) and S-(3-bromo-2-methylpropionoxyethoxycarbonylmethyl) O-ethyl xanthane (3), with an activated halide group and a xanthate group in the molecule were synthesized. The activated halide group was used as an polymerizartion of VAc. Thus, 2 was first used to mediate the radical polymerization of VAc, followed by ATRP of St, while 3 was used first to initiate the ATRP of St, followed by the RAFT polymerization of VAc. Both approaches indicate that either the radical polymerization of St or that of Vac is controlled, and well-defined PVAc-b-PSt is obtained as confirmed by gel permeation chromatography and NMR measurements.