In this study, the melting behavior of isothermally crystallized polytrimethylene terephthalate (PTT) was investigated. Multiple melting behaviors in DSC heating trace were found because two populations of lamellar stacks were formed during primary crystallization and the recrystallization at heating process, respectively. This fact could be also confirmed from the result of optical microscopy observation. The Hoffman-Weeks equation was applied to obtain equilibrium melting temperature (T-m(0)). The T-m(0) value of PTT is about 525 K, which is 10 K higher than that reported. Combining the enthalpy of fusion from the DSC result and the degree of crystallinity from WAXD result, the value of the equilibrium-melting enthalpy DeltaH(f)(0) was deduced to be approximately 28.8 kJ mol(-1).