Although there is considerable disagreement on the criterion of personal identity, most theories of personal identity agree to the view that we can be aware of something invariable and uninterrupted throughout a whole life, which we call our 'self'. But David Hume rejects this view. In Book Ⅰ of A Treatise of Human Nature, Hume argues that there is no such thing as personal identity, and we are nothing but a bundle of perceptions. According to Hume, the idea of personal identity is a fiction of the imagination. This paper attempts to examine Hume's theory of personal identity. Ⅰ will begin by examining how Hume justifies his claims. Next, Ⅰ will critically analyze some criticisms of Hume's claims. Third, regarding Hume's self-criticism in the Appendix to his Treatise, Ⅰ will investigate two possible interpretations to understanding why Hume dissatisfies with his account of personal identity. In conclusion, Ⅰ will argue that Hume's theory cannot solve the problem of the unity of consciousness.