The subject of ethics is related to our action and our experience in everyday life, so ethics has an important place in our life. The aim of this book is to examine Hume’s moral theory as expressed in his two main books, Treatise and Enquiries and to show the defects of his theory. Hume’s moral theory has been chosen, because we can find an implicit explanation of the moral sense theory in Hume’s moral philosophy. To understand Hume’s theory, it is necessary to explain some basic doctrines such as sympathy, justice, artificial virtues e.t.c. Some philosophers who influenced Hume’s thought such as Hobbes, Mandeville, Hutcheson. In this book, these philosophers also have been briefly discussed. Consequently, it is claimed that Hume’s moral theory has a heterogenous structure and also contains an ambiguity due to his conception of sympathy which has led to some misinterpretations. This book contributes the clarification of Hume’s ambiguities in his moral theory. This clarification should be useful to both students and professionals in philosophy and other human sciences fields.