Humanism is a philosophy and world view originated in Europes since the fourteenth century. It mainly concerns the advancement of humanity in contrast to the theocentric worldview of theology and the material-centered worldview of science. Just like the case in Humanism, humanity remains the main focus in Zen Buddhism, which claims that since all sentient beings have Buddha nature, everyone can achieve Buddhahood. This paper intends to reveal the humanistic spirit in Buddhism by studying the Mahayana koans (or public propositions ) and to show that same as Humanism, Zen teaching emphasizes humanity and heart to relieve all constraints on the human mind. From the three facets of the human-centered thought, the critical thinking, and the spirit of freedom in Zen koans, this paper examines the similarities and differences between Western Humanism and Zen Buddhism. It further proposes that the unique values in Zen teaching, in particular the enlightenment of the human mind, helps complement what Humanism lacks.