The cloud point curves of upper and lower consolute solutions（UCST, and LCST）have been determined for the solutions of the polydispersed polymethylmethacrylate(PMMA) and n-butyl chloride. Along with the increase of average molecular weights, the equilibrium curves of the lower consolute polymer solutions shifted toward lower temperature regions, but the upper consolute points appeared at higher temperatures. In addition, the shapes of phase boundaries near the consolute solution points became flattened at both temperature regions because of the influence of the polydispersity. In describing the phase diagram of molecular weights, both of the critical consolute temperatures were calculated, incorporating the reletive chain length and the temperature dependence for the modified Flory-Huggins interaction parameter ₁.