A xylylene diisocyanate (XDI) composition according to exemplary embodiments includes xylylene diisocyanate and an acidity regulator having a boiling point of 110 C. or higher, and the composition has an acidity of greater than 100 ppm and 1,000 ppm or less based on a total weight of the xylylene diisocyanate (XDI). An optical lens having a high transmittance and improved optical uniformity can be manufactured by controlling a polymerization reaction rate through acidity adjustment.