To investigate the effect of isomer on crystallinities of copolyimides, two copolyimides were synthesized by introducing 4, 4′-oxydianiline (4,4′-ODA) or 3, 4′-oxydianiline (3,4′-ODA) to 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA)/ 1,3-bis(4-aminophenoxy)benzene (TPER). And the mole ratio of ODA and TPER is both 1∶9. The homopolyimide based on s-BPDA/TPER/phthalic anhydride (PA) was also prepared and it was abbreviated as TPER PI. Copolyimide containing 4,4′-ODA or 3,4′-ODA was abbreviated as PI a and PI b, respectively. TGA, DSC, DMA and WXRD were used to study the crystalline behaviors and properties of the polymers. Three polymers display different cold crystallization temperatures and melting temperatures after being quenched from melts by DSC and they also display different melting behaviors after being slowly cooled from melts. Since 3,4′-ODA has more twisted structure, PI b displays the lowest melting temperature (Tm), the lowest crystallization rate, and the lowest storage modulus above Tg. After being isothermally crystallized at different temperatures for 1 h, PI a displays a triple-melting behaviors as same as TPER PI, however, PI b displays a duple-melting behaviors. Positions of some diffraction peaks of PI b were found to be changed after being isothermally crystallized at different temperatures. In a word, introduction of 4,4′-ODA and 3,4′-ODA greatly affects crystalline behaviors of the copolyimides.