Inclusion complex of decanoic acid (DA) with alpha-cyclodextrin (alpha-CyD) was prepared as an additive of cefmetazole sodium (CMZ) suppository and rectally administered to rabbits. The resulting complexation was examined by the phase solubility method, differential scanning calorimetry (DSC) and X-ray diffractometry. Plasma concentration and AUC of CMZ after rectal administration of a suppository containing DA/alpha-CyD complex to rabbits increased more significantly than those with none additive.