The analytical methods to characterize the exact chemical composition and sequence distributions of block copolymers of poly(butylene terephthalate) and poly(tetramethylene glycol) (PBT/PTMG) were reinvestigated by NMR spectroscopy. To obtain accurate information, the choice of the solvents, NMR experimental conditions, H-1 and C-13 peak assignments and the methods of calculating various sequence parameters were closely examined. For phenol-d(6)/tetrachloroethane(TCE) solutions of two copolymers having the hard segment (PBT) contents of 20 and 35wt.%, various sequence parameters were extracted from NMR spectre. In addition to that, we could accurately measure the actual number average molecular weight of PTMG segments within the copolymer by NMR. Measured average molecular weight of PTMG segments was used to calculate theoretical sequence distributions. The experimental and theoretical sequence parameters as well as chemical compositions were compared with each other.