Polyaddition of bis(4-mercaptophenyl) sulfide (BMPS) with m-phenylenebis (2-oxazoline) (MPBO) proceeded very smoothly in the mixtures of aprotic ploar solvents such as N-methyl-2-pyrrolidone (NMP) with water to produce the corresponding poly(amide-sulfide) with high molecular weights at 90 degrees C under nitrogen. The reaction of BMPS with MPBO, p-phenylenebis(2-oxazoline), and 1,4-butylenebis(2-oxazoline) was also examined in water under the same conditions, and it was found that the reaction proceeds successfully to give the corresponding poly(amide-sulfide)s with high molecular weights. These results mean that water along as well as the mixed solvents of aprotic polar solvents such as NMP with water can be uses as suitable reaction media for the polyaddition of bis(oxazolines) with dithiol to synthesize poly(amide-sulfide)s with high molecular weights.