A trial of conditioned food aversion was made to rehabilitate a young male Japanese macaque, who was habituated to artificial feeding, into wild. Aversion conditioning to apples was tried to be established by intravenous injection of cyclophosphamide (20 and 25 mg per/kg), which would be expected to induce nausea. Although this method had been succeeded in the previous studies, our trials were failed because the animal might be insensitive to cyclophosphamide or because the apple might be one of the well-habituated foods, which were reported to be inappropriate for conditioned food aversion.