The subject of this paper is probably the most influential version of moral realism, known as “moral realism naturalism”. After I propose what seems to be the most appropriate formulation of moral realism, I discuss whether it is possible to show that moral properties and natural properties can be identified a posteriori. In the second part I try to show that moral realists naturalists cannot refute wellknown Mackie’s “argument from querness” (or at least one version of that argument). In the end I discuss whether moral realists naturalists can ascribe the explanatory power to moral properties