The Sir Karl Popper`s PostDarwinian Epistemology intends to clarify an specific issue: the function of Evolutionary Theory by Charles Darwin in Sir Karl Popper`s late epistemological works. Some critics find a naturalistic turn based on biological grounds in the evolutionary epistemology, bulk of the late works of Popper. The main objective of this dissertation is to deny these interpretations. The basis of Popper`s approach to Darwinism in his epistemology is not naturalistic but logical. According to Popper, the logical structure (a priori elements) of Darwinism is the same of conjecture and refutation process of deductive reasoning. This explains why Darwinism, which is not a scientific theory but a metaphysical research program, is so fruitful and helpful to science. Hence, if we are right, the label of naturalism attributed to the late epistemological works of Karl Popper is a simple case of misunderstanding.