It has been reported that non-steroidal anti-inflammatory drugs (NSAIDs) interact with aspirin to influence its antiplatelet effect. For example, there have been reported that the rate of platelet aggregation inhibition associated with aspirin was significantly decreased when ibuprofen was taken before administration of aspirin, as compared with aspirin alone. In this study, we investigated the prescriptions on combination of aspirin with NSAIDs. The subjects were consisted of 1212 patients who were prescribed aspirin in March, 2008 in Tokai University Hachioji Hospital. The patients prescribed combination of aspirin with NSAIDs were 8.1% and 18.6% of those were prescribed in the order of adminstration to induce drug interaction. The pharmacists should provide information about drug interactions of aspirin with NSAIDs to the doctors and patients, and it is necessary to pay attention of these interactions.