The kinetics of polymer particle formation and distribution of monomers between a solution and a dispersed phase at the graft polymerization of methylacrylate onto hydroxyethyl cellulose has been studied. The particle number increases at the first stage of polymerization, then it is constant. The concentration of adsorbed monomer decreases during the polymerization process. The monomer concentration in the dispersed, phase is greater than in the solution. A mathematical model of particle formation and monomer adsorption in the polymerization process has been suggested. Some values of rate constant ratios have been calculated.