Multiple melting peaks in some semicrystalline polymers such as poly(trimethylene terephthalate) (PTT) have caused some difficulty in estimating accurately the equilibrium melting points. PTT forms a miscible blend with amorphous poly(ether imide) (PEI); for comparison purposes, a miscible system of a fixed composition (PTT/PEI of weight ratio=9/1) was determined. PTT and its miscible blend both exhibited dual melting peaks (labeled as low and high peaks: T-m,T-L, T-m,T-H), and the first peaks (T-m,T-L), not the second peak (T-m,T-H), should be used for extrapolation. The equilibrium melting temperatures (T-m(0)) of neat PTT and its blend PTT/PEI (9/1) were 245.2 and 242.4inverted perpendicularC, respectively, by the linear Hoffman-Weeks treatment using the corrected values of T-m,T-L (i.e., values obtained using a heating rate close to zero). Linear and nonlinear treatments led to a significant difference in estimated T-m(0), and the relative validity of these two methods is discussed. The nonlinear estimate yielded a higher value by about 27.3degreesC for neat PTT and 23.1degreesC for the PTT/PEI (9/1) blend, respectively (also the correction in T-m,T-L at the same condition mentioned previously). Results showed melting depression in miscible PTT/PEI (9/1). In addition, the T-m(0) value of neat PTT was higher than that of PTT/PEI (9/1) owing to much thicker and more-perfect crystals in neat PTT.