The purpose of the paper is to examine critically the validity of eudaimonics and naturalized Buddhism based on neurophysicalism and subjective realism developed by O. Flanagan. The discussion proceeds in the following order. In chapter 2, I discuss the main contents of Flanagan’s neurophilosophy in relation to reductive physicalism and neurophenomenology, which are in competition with it. In chapter 3, I deal with the origins of Aristotle s concept of eudaimonia, and then examine Buddhist happiness and Buddhist eudaimonia suggested by Flanagan and discuss the relationship between them. In chapter 4, I examine the naturalized Buddhism. Flanagan suggests Four Noble Truths, Three Roots, and Three Learning as the central tenets of naturalized Buddhism which does not include supernatural realities and concepts. I point out the problematic part of his naturalization and examine the significance of naturalizing Buddhism. Finally, in chapter 5, I discuss enactionism and neurophenomenology as alternative theories to overcome the limit of Flanagan’s neurophilosophy and point our the difference between the two theories and Flanagan’s misunderstanding of neurophenomenology.