Crystals of a purine nucleoside compound, particularly crystals of 2',3'-dideoxyinosine, which have excellent storage stability and have a concentration of phosphate attached to the crystal of 25 ppm or more, may be produce by: (1) preparing an aqueous solution containing phosphate ion (PO.sub.4.sup.3-) and a purine nucleoside compound; and (2) crystallizing the purine nucleoside compound from the aqueous solution.