To understand the mechanism of polymer epitaxy during solution polymerization (polymerization-induced epitaxy, PIE), the kinetics of the epitaxial film growth was compared with that of polymerization in solution. The surface coverage and the domain size of epitaxial films as well as the molecular weight of the polymer formed in solution were examined as functions of the reaction time, the monomer concentration, and the initiator concentration. Atomic force microscopy was used to evaluate the coverage and the apparent island size distribution. Cationic ring-opening polymerization of tetrahydrofuran (THF) in dichloromethane at 0 degrees C on a graphite substrate in the reaction mixture induces an epitaxial film of poly(THF), consisting of 0.5 nm thick, flat, rectangular islands. The reaction time dependence indicates that the film has developed much faster than the polymer growth in solution. When the monomer concentration was varied, no polymer was formed in solution below 3 mol/L, corresponding to the equilibrium monomer concentration. The well-developed PIE film was formed even below this concentration. This result proves that PIE is not an adsorption of the polymers that have first formed in solution. At low initiator concentrations, the polymerization in solution was significantly disturbed due to side reactions, while the PIE film developed well at all concentrations without noticeable dependence on the initiator concentration. This shows that the polymerization reaction responsible for PIE is minimally affected by termination or chain transfer reactions. The kinetics suggests a possibility of the monomer concentration enhancement near the surface. On the basis of these results, a positive feedback model of polymerization with epitaxial adsorption through conformational constraint is proposed as a PIE mechanism.