A series of poly(m-methylene 2,6-naphthalate-co-1,4-cyclohexylenedimethylene 2,6-naphthalate) copolymers were synthesized, and their crystallization behavior was investigated using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Poly(ethylene 2,6-naphthalateco-1,4-cyclohexylenedimethylene 2,6-naphthalate) (P(EN-co-CN)) copolymers do not crystallize in the middle of copolymer composition, whereas poly(buthylene 2,6-n phthalate-co-1,4-cyclohexylenedimethylene 2,6-naphthalate) (P(BN-co-CN)) and poly(hexamethylene 2,6-naphthalate-co-1,4-cyclohexylenedimethylene 2,6-naphthalate) (P(HN-co-CN)) copolymers show clear melting and crystallization peaks in DSC thermograms and sharp diffraction peaks in WAXD patterns for all copolymer compositions, indicating that both P(BN-co-CN) and P(HN-co-CN) copolymers show cocrystallization behavior. Furthermore, P(BN-co-CN) copolymers exhibit an eutectic melting point in the plot of melting temperature vs copolymer composition, and their WAXD patterns are divided into two classes according to the copolymer composition, i.e., PBN-type and PCN-type diffraction patterns. This indicates that P(BN-co-CN) shows isodimorphic cocrystallization. On the other hand, the melting temperature of P(HN-co-CN) copolymer increases continuously with increasing CN content without showing an eutectic melting temperature, indicating that P(HN-co-CN) copolymer shows isomorphic cocrystallization behavior.