The present invention provides an aqueous suspension preparation which contains (3aR, 4S, 7R, 7aS)-2-{(1R, 2R)-2-[4-(1, 2- benzoisothiazol-3-yl)piperazin-1-ylmethyl]cyclohexylmethyl}hexahydro-4, 7-methano-2H-isoindole-1, 3-dione (compound 1), a pharmaceutically acceptable acid addition product thereof or a mixture of the compound and the acid addition product as an active ingredient, and which has the feature (I) or (II) described below. (I) In cases where a thickening agent is contained in the preparation, the circularity of suspension particles is about 0.960 or less. (II) In cases where a thickening agent is not contained in the preparation, the circularity of suspension particles is about 0.945 or less.
