AbstractGalactomannan gum isolated from the seeds of sesbania was subjected to chemical modification via carboxymethylation in non-aqueous medium using monochloroacetic acid under the catalytic action of sodium hydroxide. The obtained derivatives were subjected to measuring the degrees of substitution (D.S.), rheological properties of their pastes, and evaluated as thickeners in printing cotton fabrics with reactive dyes. Highly substituted derivatives could be used successfully as thickening agents in printing cotton fabrics either alone or in admixture with sodium alginate. Prints acquire soft handle, colour strength (K/S), and fastness properties nearly identical to corresponding samples that were printed using sodium alginate.