This article examines the relationship between economic rationality and the possibility of a moral science of business ethics. The purpose of this inquiry is to consider whether a universal and non-controversial moral science of business ethics can be defined satisfactorily, and linked to economic rationality of managers and other stakeholders of firms operating in market economies. Economic rationality connotes economic efficiency, meaning a strictly instrumental maximization of actor utility from limited resources. This rationality is a universal and value free (or (...) value neutral) axiom: actors should and generally will be rationally efficient. Utilitarianism accepting aggregation across values is the moral framework associated with market exchange. Business ethics is about normative valuation of motives, actions, and consequences. This article argues that the common foundation across relevant ethical frameworks – moral common sense, Kantianism, virtue theory, religion as a belief system, and utilitarianism – is a first or axiomatic principle of no harm without acceptable justification. A moral science of business ethics proceeds from this no harm axiom. (shrink)