The present invention provides a combination preparation which comprises: a prior-release section comprising aspirin or a pharmaceutically acceptable salt thereof as a pharmacologically active component; and a delayed-release section comprising clopidogrel, an isomer thereof or a pharmaceutically acceptable salt thereof as a pharmacologically active component. The combination preparation of the present invention exhibits a far better effect in preventing platelet aggregation than does simultaneous oral therapy or treatment with the respective single preparations, and not only can it improve the patient's drug-taking compliance by administration once a day but it can also reduce the adverse reactions which follow long-term administration of aspirin. The combination preparation of the present invention is also advantageous in that it exhibits an outstanding effect in inhibiting blood platelet aggregation despite a reduction in the amount of aspirin ingested, and in that it converts clopidogrel resistance into susceptibility and prevents serious adverse reactions caused by clopidogrel resistance and in that it can be stored over the longer term since it is stable under common storage conditions.