PURPOSE: To obtain a novel thiol derivative which has high refractive index, gives cured products excellent in transparency and can be used as a raw material for optical materials, coating materials and adhesives. CONSTITUTION: This thiol derivative is shown by formula I. This compound is obtained by reaction of (A) bis(4-mercaptophenyl)sulfide with (B) an allyl halide such as allyl chloride in the presence of an alkali at 0-70 deg.C, preferably 10-40 deg.C. In this reaction, the component B is used in an amount of 1-1.5 equivalent amount, preferably 1-1.2 equivalent amount per 1 equivalent amount of the component A. In addition, this thiol derivative is shown by formula II. This thiol compound of formula II is prepared by reaction of (C) bus(4-(2,3- epoxypropylthio)phenyl)sulfide with (D) thiourea or a thiocyanate salt at 0-80 deg.C, preferably 10-60 deg.C where the amount of the component (D) is a 1-4, preferably 1-3 equivalent per one equivalent of the component (C).