Stable crystals of an acid addition salt of an optically active thienotriazolodiazepine compound or its hydrate of the formula

wherein R 1 is hydrogen, R 2 is 2-phenylethyl substituted by alkyl having 1 to 5 carbon atoms, 2-morpholinocar- bonylethyl or alkyl having 6 to 12 carbon atoms, or R 1 and R 2 may combinedly form a saturated 5-membered ring having one substituent selected from the group consisting of morpholinomethyl, morpholinocarbonyl and N,N-dipropylcarbamoyl, R 3 is halogen, alkyl having 1 to 5 carbon atoms or alkoxy having 1 to 5 carbon atoms, R 4 is trifluoromethyl or alkyl having 1 to 5 carbon atoms, R 5 is hydrogen or methyl, m is 1-2, and n is 0-2. The present invention provides optically active thienotriazolodiazepine compounds having strong PAF-antagonistic activity as markedly stable crystals which are excellent in crystalline property, permit purification by recrystallization, and have high chemical purity and optical purity, thereby rendering industrial large-scale synthesis attainable. In addition, crystallization thereof facilitates medicinal standardization and pharmaceutical formulation.