Radical polymerization behaviors of vinyl acetate (VAc), initiated by N, N-azobisisobuty-ronitrile(AIBN) in the presence of several alkyl iodides(RI) such as chloroiodomethane(CIM), iodoform, and tridecafluorohexyliodide(TDFHI) have been investigated. Living natu.e, i.e., a fairly good agreement between the number average degree of polymerization of the resulting polymer (DP$_{n}$) and the theoretical value, determined by the molar ratio of VAc and RI, which is based on the assumption that one polymer molecule is formed by one molecule of RI. A linear relationship is observed between % conversion and DP$_{n}$ is observed when the molar ratio of AIBN/RI is kept at 2. The MWD of the resulting polymer decreases as % conversion increases. Polymers having narrow molecular weight distrbution (DP$_{n}$DP$_{n}$ <1.5) are obtained in the late. stage of polymerization. However, experimental DP$_{n}$ values show deviation from the theoretical values in the early stage of polymerization. This leads us to the conclusion that the living nature of the system is ascribable to the stabilization of the active propagating radical species by rapid iodine exchange with RI followed by the establishment of equilibrium between the active propagating radical species and polymer having a dormant carbon-iodine terminal group. The factors resulting in the loss of the living nature have also been discussed in conjunction with the results obtained from photo-induced polymerization.erization.