The photodissociation of several N,N-diethyldithiocarbamate derivatives (RDC), i.e., benzyl, 1-phenylethyl, 2-phenylethyl, n-butyl, sec-, and tert-butyl N,N-diethyldithiocarbamates, was investigated by the spin trapping technique to elucidate the polymerization mechanism of styrene (St) with RDC as iniferters. The scission of RDC occured at two different C-S bonds depending on the structure of the alkyl groups of RDC and the cleavage manner was dominated by both resonance and steric effects. It has been confirmed that RDC generating an N,N-diethyldithiocarbamyl radical acts as an effective iniferter and induces the living radical polymerization of St in homogeneous system. The polymerizations of St with tetraethylthiuram disulfide and p-xylylene bis(N,N-diethyldithiocarbamate) were also discussed on the basis of the results of the spin trapping for RDC as the model compounds of the poly(St) chain ends.