This Thesis deals with the Kant's arguments on the right to lie, which are one of the his criticized issues. This criticism came from his essay, “Üer ein vermeintes Recht aus Menschenliebe zu Lüen”( = “ein Recht zu Lüen”), in which he said the duty of veracity unconditioned. But his arguments in Die Metaphysik der Sitten and Eine Vorlesung Kants üer Ethik vary from those in “ein Recht zu Lüen”. While he hold a strict rigorism about the duty of veracity in the latter essay, he do not so in the former works. The following two questions are the important contents that we want to make clear in this Thesis. (1) Whether are Kant's arguments on lying consistent throughout his all writings? (2) Can we accept Kant's conclusions about lying, under our common senses? To solve these questions, we will examine Kant's main works, Grundlegung zur Metaphysik ser Sitten( = Grundlegung) and Kritik der praktischen Vernunft, in addition to the above three writings. Basing on his insistence in “ein Recht zu Lüen”, we will reconsider the arguments about lying that was presented in his other works. And we will try to find a solution to second question in a concept, 'perfect duty', that Kant made mention of in Grundlegung.