The polycondensation of bis(4-mercaptophenyl) sulfide (BMPS) with bis(4-chloro-3-nitrophenyl) sulfone (BCNPS) was examined using various organic or inorganic bases in mixed solvents of N-methyl-2-pyrrolidone (NMP) with water or in plain water. The reaction of BMPS with BCNPS proceeded smoothly to give the corresponding polysulfide in mixed solvents of NMP with water at 60 degrees C using 1,8-diazabicyclo[5.4.0] undecene-7 as a base, although the rate of the reaction decreased gradually as the water in the solvent increased. Polysulfide can also be obtained by reaction in plain water using appropriate organic bases such as tripropylamine (TPA) or quinoline. The polysulfide with a number-average molecular weight of 45,100 was synthesized in 62% yield when the reaction of BMPS with BCNPS was performed using TPA as a base at 60 degrees C for 48 h in plain water.