Conversion to polymer and molecular weight of grafted copolymer in the graft copolymerization of styrene initiated by the xanthate method is strongly dependent on reaction conditions even in the range of agitation speed when the effect of diffusion of monomer is neglected. When sulfuric acid and hydrogen peroxide are added simultaneously after 15 min of purging with nitrogen 99.99%, conversion and molecular weight vary little with stirring speed. Both parameters decrease with increasing stirring speed when H2 SO4 is added 1 min earlier than H2O2 and nitrogen is purged 15 min before starting the reaction. Both parameters increase when H2SO4 and H2O2 are added simultaneously after 60 min of purging with nitrogen. Highest conversion is observed when both reagents are added after 15 min of purging with nitrogen. Molecular weight is the highest at 310 rpm when H2SO4 is added 1 min earlier than H2O2, and at 1100 rpm when nitrogen is purged for 60 min.