This article discusses Nishida's ideas of self-awareness, knowledge, and rationality, construing them as raising epistemological problems called "self-knowledge." Although the term "self-knowledge" signifies significantly varying problems within different philosophical traditions, the logic and argumentation behind them are often analogous, and it is on this resemblance that this article concentrates. It is argued here that the issues Nishida raises concerning knowledge of oneself as an agent are broader than those discussed in the contemporary Anglophone epistemology, and this broader concept of self-knowledge constitutes one of the central themes in Nishida's philosophy as a whole. Specifically, two versions are examined of the so-called "rationality" thesis with regard to self-knowledge and first-person authority in analytic philosophy (the basic and modified rationality theses), and these are compared with relevant notions in Nishida's theories of knowledge and self-awareness. The theories of Tyler Burge (the rationality thesis) and Richard Moran (the modified rationality thesis) are discussed, and the latter's self-commitment theory is regarded as having some similarity with Nishida's basic position. There are three levels in Nishida's account of self-awareness/self-knowledge: epistemic self-awareness, volitional self-awareness, and the so-called "noumenal self." This last notion, in which Nishida often describes the self as "place," entails his rationality thesis, namely that reason and first-personhood are deeply involved in one another, both postulating the noetic (non-cognitive) noumenal self-awareness.