Nylon 6-poly(ethylene glycol) -nylon 6 type block copolyrners(PEG-b-nylon 6) were prepared by anionic copolymerization of $varepsilon$-caprolactam and $varepsilon$-caprolactam-blocked PEG-hexa-methylene diisocyanate prepolymer with NaH. In this anionic polymerization process, it was possible to increase the polymerization reaction rate at lower temperature than that of the condensation polymerization process employed commercially in the nylon 6 production. It was shown that the molecular weight of PEG-b-nylon 6 is higher than that of a commercial nylon 6 and is increased with increasing the PEG content in the block copolymer.