This study explores the importance of Fahreddin Râzis in history of Islamic logic and his vievs on some matter concerning logic. The importance of Razi lies in his acceptance of the logic as an independent dicipline and also his use of it in Islamic Theology systematically. After dealing with Razi’s importance in the history of Islamic logic, we mainly focus on his thought about syllogism, definition, categories and some other subjects of logic. It should be noted that among all these subjects, Theologions opinions about the categories are worth mentioning