A reactive dye composition comprising at least one alkylnaphthalenesulfonic acid/formaldehyde condensate and a compound represented by the following formula, ##STR1## wherein D is an organic dye residue having at least one sulfo group, R.sub.1 and R.sub.2 are independently a hydrogen atom or a C.sub.1 to C.sub.4 alkyl group unsubstituted or substituted with a halogen atom or a hydroxy, cyano, alkoxy, carboxy, carbamoyl, alkoxycarbonyl, alkylcarbonyloxy, sulfo or sulfamoyl group, A is a phenylene group unsubstituted or substituted with one or two substituents selected from chlorine and bromine atoms and methyl, ethyl, methoxy, ethoxy and sulfo groups, or a naphthylene group unsubstituted or substituted with one sulfo group, X is a halogen atom, and Y is --SO.sub.2 CH.dbd.CH.sub.2 or --SO.sub.2 CH.sub.2 CH.sub.2 Z in which Z is a group capable of being split by an alkali, which composition is very readily soluble in water and aqueous alkaline solution, so that a dyeing or printing of cellulose fiber materials can be effectively carried out even by one-bath pad dyeing or one-phase printing methods to give a dyed product of a deep color having excellent levelness and no speck.