In order to assess the recent suggestion of Hawker et al.(1) that the C-ON bond of an alkoxyamine is weakened by acetic anhydride (Ac2O), the activation (dissociation) rate constant k(act) of a polystyrene-nitroxide adduct was directly determined in the presence of Ac2O. The result showed that Ac2O has no effect on the activation rate, contrary to the suggestion. On the other hand, Ac2O was confirmed to accelerate the polymerization rate. The mechanism of acceleration was discussed.