PURPOSE: To impart a soft feel and excellent hydrophilicity without causing yellowing by conditioning fibers with a composition containing a specific polydiorganosiloxane.

CONSTITUTION: A composition prepared by emulsifying a polydiorganosiloxane containing at least two structural units of formula I [X is selected from formula II (R' is a linear or a branched 2-8C alkylene; R" is selected from H or a 1-6C alkyl); R is selected from phenyl, 3,3,3-trifluoropropyl and a 1-4C alkyl; (a) is 1 or 2; (n) is 1-10; (t) is 0 or 1], e.g. a compound represented by formula III (X and R are each same as that described above; Y is X or R; (p) is, e.g. 5-1,000; (q) is 1-100) is used to condition synthetic fibers. Thereby, the resultant textile substrate is excellent in soft feel and manifests good hydrophilicity. The composition is excellent in storage stability.