Moral metasemantic theories explain how our moral thought and talk are about certain properties. Given the connection between what our moral terms are about and which moral claims are true, it might be thought that metasemantic theorising can justify first-order ethical conclusions, thus providing a novel way of doing moral epistemology. In this paper, we spell out one kind of argument from metasemantic theories to normative ethical conclusions, and argue that it fails to transmit justification from premises to conclusion. We give three reasons for this transmission failure, which together pose a serious challenge to such metasemantic arguments.Moral metasemantic theories tell us in virtue of what our moral thought and talk pick out a property. 1 Because of this foundational role in fixing what our moral terms are about, metasemantic theories seem to yield a distinctive way of doing normative ethics: we simply argue from the metasemantic theory, plus the premise that a certain descriptive property fulfils the theory's reference-determining conditions, to the conclusion that this descriptive property co-occurs with a moral property. In this paper, we spell out and critically examine this way of theorising -which we call metasemantics-first moral epistemology. We argue that such theorising faces serious challenges.1 Metasemantic theories tell us about (1) what makes it the case that terms or sentences are about a certain property/object, or (2) what makes it the case that concepts or beliefs (psychological representations) are about a property/object. Our discussion is largely framed around (1) but everything we say could be put in terms of (2). We will remain neutral in this paper between referentialist (Braun 2016; Edwards 2014) and non-referentialist (Chalmers 2011; Segal 2000) views of content, which differ on whether the content of a term or concept is exhausted by its referent.