To obtain a hardly soiled nylon fiber hardly forming a soil with a dyestuff at a room temperature but capable of being dyed at a high temperature, and useful as a carpet raw material by covering a specific soil-blocking agent on its surface.

This aqueous finishing agent is prepared by blending a soil- blocking agent selected from a condensed polymer product consisting of a recurring unit expressed by formula I [R is H, SO3X (X is H or a cation), formula II or III], containing SO3X by at least 40% and a bond shown by formula IV by at least 40%, and a mixed condensation product of naphthalene sulfonic acid with dihydroxydiphenylsulfone and formaldehyde, and a fluorine compound such as a reaction product of N-ethylperfluorooctylsulfonamide ethanol with toluidine isocyanate. A nylon fiber hardly soiled but capable of being dyed and showing almost zero dye absorption test value at 25°C but ≥30% value at ≥100°C, is obtained by spinning nylon 6, 6 of 8-24 de fineness, imparting the above aqueous finishing agent and then stretching.