Two series of ,trans,-1,4-poly(butadiene-co-isoprene) copolymers (TBIR) were prepared using the catalyst system TiCl,4,/MgCl,2,-Al(,i,-Bu),3, at different reaction temperatures. All dyad and triads sequence distributions, the number-average sequence length and the sequence concentration of the copolymers were calculated according to ,13,C-NMR spectra. The influences of temperature and initial molar ratio of butadiene to isoprene (Bd to Ip) on the distribution of the chain segments in the TBIR copolymers were discussed. The correlation of copolymer compositions and thermal properties were also evaluated, which facilitated the understanding of controlling the degree of crystallinity and the transition temperature by changing Bd content and temperature.