A reactive polysaccharide derivative of formula (1a) or (1b), in which A is —O—, —S— or (1c), Q1 is hydrogen, the radical —B—A—Z, C1-C10aryl which is unsubstituted or substituted, C1-C12alkyl which may be interrupted by oxygen and is unsubstituted or substituted, Q2 and Q3 are each independently of the other hydrogen, C1-C12aryl which is unsubstituted or substituted, C1-C12alkyl which may be interrupted by oxygen and is unsubstituted or substituted, B is an aliphatic or aromatic bridge member, Z1 and Z2 are each independently of the other a reactive radical of the vinylsulfonyl series, the haloacryloyl series or the heterocyclic series, PS is a polysaccharide radical, m is 0, 1 or an integer greater than 1, n is 1 or an integer greater than 1, and the sum of n+m corresponds to the original number of hydroxy groups in the polysaccharide molecule, is useful as a finishing agent for textile fibers and for other applications.