These paragraphs below are extracted from the first chapter of G. E. Moore’s Principia Ethica（1903） which titled as “The Subject-Matter of Ethics”. As the title of this chapter has shown，Moore’s primary concern in which is to elaborate the scope and object of Ethics and also its characteristics，that is to say，what is the goal of ethical inquiring and how to achieve to it. With this in hand，Moore analyzed several fundamental questions in the following part such as the property of ethical judgments，the relationship between action and the object of ethical research，the definition of Good，what is the role of conception Good played in ethics and so on. After that，he reached the conclusion that Good is the most important notion of Ethics and Good cannot be defined.