PURPOSE: To obtain a cyclic sulfite compound useful as a raw material, etc., for contact lenses from an epoxy compound having a polymerizable group by reaction in one stage.

CONSTITUTION: An epoxy compound of formula I or II [R1 is H or methyl; R2 to R8 are each independently H or a lower alkyl; both R3 and R4 or R7 and R8 together may respectively form a ring; (n) is an integer of 1-10; (p) and (m) are each independently 0 or 1] having a polymerizable group, etc., e.g. glycidyl (meth)acrylate is reacted with sulfur dioxide under conditions without substantially causing polymerization reactions of either of the epoxy compound and the produced cyclic sulfite compound to afford the subject cyclic sulfite compound containing the polymerizable group, e.g. 1,3,2-dioxathiolan-4- ylmethyl 2-oxide methacrylate. The reaction is preferably carried out in the presence of a polymerization inhibitor without using a polymerization catalyst.