A cephalosporin antibiotic, PATC (5-Amino-2-[((6R,7R)-7-{(2Z)-2-(5-amino-1,2,4-thiadiazol-3-yl)-2-[(1-earboxy-1-methylethoxy)imino]acetylamino}-2-carbo xy-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-en-3-yl)methyl]-1-(2-hydroxyeth yl)-1H-pyrazol-2-iumchloride; MW 632.1 Da), was crystallized by neutralization method, and the spherical agglomeration of micro crystals was obtained to develop a drug for injection. The morphology of agglomerates depended on the initial super-saturation ratio and the presence or absence of seed crystals. Spherical agglomerates were obtained by adding seed crystals of 0.1 wt % under a high initial super-saturation ratio of 130. The compactly packed spherical agglomerates were composed of a number of rod-shape crystals with a uniform length of 60 mu m, and had good filtration property. The specific volume of spherical agglomerates was 1.75 cm(3)/g.