A cyclic sulfur compound represented by the formula, ##STR1## wherein R is --CH.sub.2 CH.sub.2 O).sub.n CH.sub.2 CH.sub.2 --, m is an integer of 2 to 4 and n is an integer of 1 to 3 is novel and can be used as a crosslinking agent instead of sulfur per se and also as a monomer for preparing polysulfide polymer. Said cyclic sulfur compound can be produced by reacting a metal sulfide represented by the formula, ##STR2## wherein R is the same as defined above, R' and R" are independently selected from alkyl groups and aryl groups and M is silicon or tin, with a halogen, sulfur dichloride or sulfur monochloride.