The insertion reaction of propylene sulfide (PS) into p-tolylcarbamothioate (PTCT) was examined in the presence of tetrabutylammonium chloride (TBAC) in 1-methyl-2-pyrrolidinone at 60 degrees C in the feed ratio of PTCT/PS = 1/1-1/40, affording the corresponding polysulfides in satisfactory yields. It was found that the molecular weights (M-n's) coincided with the feed ratios PS and molecular dispersity ratios (M-w/M-n) were very narrow (M-w/M-n < 1.10). i.e., this insertion reaction could be performed under the living system. Furthermore, the insertion living reaction of PS using tricarbamothioate was examined to give the controlled three-arms star-shaped polysulfides.