The problem of the present invention is to provide an anti-tumour agent of a salt of 1-(2-deoxy-2-fluoro-4-thio-&bgr-D-arabinofuranosyl)cytosine. The salts of the anti-tumour agent provide at least one of the following characteristics: (1) anti-tumor activity (2) crystallinity (3) water solubility (4) are not deliquescent (5) provides fluidity (6) provides tableting properties (7) can be produced under environmentally friendly conditions and (8) can be mass-produced on scale-up.
