Nowadays, patients usually take more than three drugs for diseases such as hypertension, diabetes, and dyslipidemia. Hence, nuclear medicine physicians should be very careful about the medication history of each patient and ensure that their medication will not cause false positive or false negative imaging results, because either condition will interfere with adequate treatment of the patient and result in a wrong diagnosis. The aim of the present paper is to develop an ontology-based medication search and alert system for scintiphotography of Chang Gung Memorial hospital at Kaohsiung. Composed of four sub-systems, including Medication History Collect Agent (MHCA), Medication History Search System (MHSS), Patient Medication Consultation System (PMCS), and Patient Medication Alert System (PMAS), this medication search and alert system for scintiphotography is expected to support decision making of nuclear medicine examination, improve accuracy of image reading, and offer detailed data for further research. The ultimate goal of this system is to ensure patient safety.