Molecular weight (M) dependence of the lateral growth rate (V) of folded chain crystals (FCCs) of polyethylenes (PE) was investigated. This study was carried out on single (or single crystal-like) crystals using the equilibrium melting temperature (T-m(0)) determined by applying Gibbs-Thomson＇s equation. The well-known relation V = V-0 exp( - B/Delta T) was obtained where V-0 and B are constants and Delta T is a degree of supercooling. V-0 strongly decreased with increase of M, whereas B did not, which indicates that the self-diffusion process of polymer chains mainly controls the M dependence of V, whereas the nucleation one does not. Experimental formula that V proportional to V-0 proportional to D proportional to M-H where D is self-diffusion constant and H is a constant; H = 1.7 was obtained. These results are similar to Hoffman et al.＇s results but their H was rather smaller, H = 1-1.5. A similar study on extended-chain single crystals (ECSCs) reported in our previous paper gave the same experimental formula but H was much smaller, H = 0.7. From the difference in H between FCCs and ECSCs, a new proposal that M dependence of V may be mainly controlled by the surface diffusion process of chain polymers on the growing crystal surface, is discussed briefly.