The present invention relates to a reactive printing dye composition, which includes: (a) at least one reactive dye; (b) an organic buffer; and (c) a mirabilite or a dispersant. The reactive printing dye composition of the present invention is capable for being used in the fabric-dyeing, for example, dyeing of cotton, hemp, silk, rayon, wool, blending, etc. The reactive printing dye composition of the present invention is advantageous in high pH value stability, high storage stability, and reduced degradation in dyeing strength. In addition, the present invention further provides an aqueous reactive printing dye composition.