The present invention relates to a crystal of 1-ethyl-7-methyl -3-{4-[(3-methyl-3H-imidazo[4,5-b]pyridin-2-yl)oxy]phenyl}-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one useful as a prophylactic or therapeutic agent for schizophrenia and the like, which shows an X-ray powder diffraction pattern having characteristic peaks at interplaner spacings (d) of 13.59±0.2 and 6.76±0.2 Angstroms in powder X-ray diffraction.本發明係關於可用於作為精神分裂症等的預防或治療劑之1-乙基-7-甲基-3-{4-[(3-甲基-3H-咪唑并[4,5-b]吡啶-2-基)氧基]苯基}-1,3-二氫-2H-咪唑并[4,5-b]吡啶-2-酮的結晶，其於粉末X-射線繞射顯示具有平面間距(d)為13.59±0.2及6.76±0.2埃(Å)的特徵峰的X-射線粉末繞射圖案。
