Various segmented block copolyetheramides based on nylon 6 and polyoxypropylene (POP) were synthesized by melt polymerization of caprolactam (CPL) and polyoxypropylene diamines (POPD) as a function of the size and content of POPD. As the content of POPD in the feed increased, the IR absorption band at 1110 cm-1 increased. The H-1-NMR analysis indicated that peaks characteristic of methylene groups in POP unit appeared at 1.2, 3.6, and 3.8 ppm. The compositions of the hard and soft segments in the block copolymer were determined from the NMR data. The POP content in copolymer was higher than that in the feed due to the removal of unreacted CPL by water extraction. The average block lengths of the hard and soft segments were calculated from molecular weights and copolymer compositions.