This paper attempts to explain the relationship between the concepts of democracy, justice and peace in political thought. Popper's critical and liberalist approach toward democracy impelled us to utilize this twenties-century's political philosopher's view in explaining democracy, justice and peace. Popper's critical view in the field of philosophy of science has shown its reflection in social context. Criticizing the intellectual foundations of violence, dictatorship and authoritarianism, Popper considers the democracy based on open society as a proper ground for promoting justice and peace. On the other hand, Popper's view on peace and justice and, at a higher level, democracy, is very close to that of the international organizations engaged in promoting human rights. Therefore, Popper's critical rationalism offers an appropriate framework for explaining the relationship between democracy, justice, and peace.