Poly(pentamethylene 2,6-naphthalate) (PPN) with a intrinsic viscosity of 0.69 dl/g was synthesized from dimethyl 2,6-naphthalene dicarboxylate and 1,5-pentnandiol via a two-step process of transesterification and polycondensation using a high pressure reactor. Manganese acetate tetrahydrate and tetraisopropyl orthotitanate were used as catalysts for transesterification and polycondensation, respectively. Melt-quenched films of the PPN were prepared and annealed under various conditions, and the thermal properties of the annealed films were characterized by using a DSC and synchrotron WAXS. PPN exhibited a very slow crystallization rate. On DSC thermograms, three melting peaks were observed at around $100{sim}125^{circ}C$, depending on the annealing conditions. At least more than 6 hours of annealing was needed for the PPN film to be crystallized when it was annealed at a temperature below its melting point, and 3 hours of annealing when annealed at $100^{circ}C$ which corresponds to the $T_{ml}$. From the results of DSC and WAXS analysis, it is deduced that the continuous increase in crystallinity of PPN with increasing annealing time comes from the increase in the number of crystallites, not from the increase in the crystallite size.