Disposition profile of ampicillin (ABPC) among honeybees, larvae, honey and royal jelly in a hive after oral dosing to adult bees was studied. Four honeybee colonies were administered the single dose of ABPC at the rate of 30 mg/hive by addition to sugar syrup or pollen substitute (paste) for 1 day intake. The colonies received ABPC in syrup showed high drug residue levels in honey and it lasted over 14 days beyond the detection limit of residual analysis. In the hives given ABPC in paste, relatively low honey residues were found, however, the distributions of the drug in young larvae and jelly which was the food of the larvae were very low. ABPC was considered to be a promising drug for the control of American foulbrood, an important bacterial disease of honeybee larvae, because of its high antibacterial activity to the pathogen, Paenibacillus larvae, and instability of residue in honey as human food. The low distribution in young larvae, the target of the disease, threw a doubt on the efficacy of ABPC for American foulbrood control.