This invention provides a polymerizable composition for a lens with a high refractive index comprising at least one polythiol compound represented general formula (1): Rnull(SH2SH)n nullnull(1) where R is an organic residue except an aromatic group and n is an integer of at least 1, having at least two intramolecular mercapto groups and at least one compound having an intramolecular functional group which can react with a mercapto group; a resin prepared by polymerizing the composition; an optical element and a lens made of the resin; and a process for preparing a thiol compound comprising the steps of reacting a compound represented by general formula (2): HSnullR1(nullSnullR2)m nullnull(2) where m is an integer of at least 1; R1 represents an aromatic, aliphatic, alicyclic or heterocyclic organic residue or aliphatic, alicyclic or heterocyclic organic residue with an aromatic ring or a sulfur atom in its chain; and R2 represents a protective group, with a compound having a functional-group which can react with a mercapto group, and then converting nullSnullR2 into nullSH.