本文以利瑪竇《交友論》和衛匡國《逑友篇》為例談友道，所持理由有二，為何利瑪竇《交友論》（1595）對中國士人帶來震撼和關注，此其一。衛匡國與祝石談及利瑪竇《交友論》為何認為該書未備「未盡友義之深之博」，遂作《逑友篇》（1647）擴充友道內容，此其二。本文依序探討（一）前言：中國士人是否鮮少注意五倫之末朋友倫？為何《交友論》和《逑友篇》對中國士人帶來震撼和關注？（二）友道之根：據德相友及信、愛；（三）友處之方：不求非義與毋偽毋疑；（四）益友朂培德：察其所愛、忠告責善改過；（五）結語：本文通過《交友論》和《逑友篇》探討掌握到友道之根，友處之方，益友朂培養愛德臻至善，可以提供現代人交友之道不同的思考途徑。

In this paper there are two reasons to taking Matteo Ricci’s Jiao You Lun (《交友論》, On Friendship, 1595) and Martino Martini’s Qiu You Pian (《逑友篇》, Pamphlet on Gathering Friends, 1647) as examples discussion on the principles of friendship. The first one is, why did Matteo Ricci’s Jiao You Lun astonish Chinese Scholars and attract their attention? The second one is, since Martino Martini and Chu Shih (祝石) considered that “the contents of Ricci’s Jiao You Lun did not covered completely regarding the depth and broadness of the meaning of friendship,”they wrote Qiu You Pian to increase and broaden the contents of the principles of friendship. This paper aims to explore five sections as following: (1) Preface: did Chinese scholars seldom pay attention on the relationship of friends, the last relationship among wu lun? Why did Jiao You Lun and Qiu You Pian astonish Chinese Scholars and attract their attention? (2) The foundation for the principles of friendship: people should choose a friend with one’s virtue, sincerity, philia. (3) Ways to with friends: maintain friendship without injustice and unrighteousness, no-fake and no-doubt. (4) Good friendship develops the cultivation of virtue: a discussion on how to examine in what things your friend prefers, faithfully admonish and lead your friend to choose what is good, and to correct one’s mistakes. (5) Conclusion: by taking Matteo Ricci’s Jiao You Lun and Martino Martini’s Qiu You Pian, this paper explores the foundation for the principles of friendship, ways to with friends, and how good friendship develops the cultivation of love in order to achieve the highest excellence. This paper is to provide the moderns with a different way of thinking on the principles of friendship.