PURPOSE: The aimed yarn having stability to deterioration and coloring when it is exposed to sunlight, a chlorine bleacher, a combustion gas, heat, etc., obtained by adding a specific phenolic compound as a stabilizer to yarn.

CONSTITUTION: 100pts.wt. polyurethane is blended with preferably 0.5W10pts.wt. phenolic compound shown by the formula (R1 is 1W6C alkyl; R2 is 4W9C alkyl, cycloalkyl, or aralkyl; R3 and R4 are H, or methyl; n is 0W3) as a stabilizer, to give the aimed polyurethane elastic yarn. The compound shown by the formula, for example, is obtained by condensing a p-alkylphenolic compound with dicyclopentadiene, and reacting the condensate with isobutylene.