Hydrochloride crystal of 5-chloro-6-[(2- iminopyrrolidin-1-yl)methyl]pyrimidine-2,4 (1H, 3H)-dione monohydrochloride on which powder X-ray diffraction the peaks are marked at two or more angles selected from 10.5°, 19.6°, 23.7°, 26.2° and 31.2° (20±0.1˚) diffraction angle and pharmaceu¬tical composition on basis of said crystal. Table: 3