Are the two philosophical prescriptions for the perfection of our life, Kierkegaardian religiosity and Kantian morality compatible? How compatible are religious belief and philosophical reason? In this paper I am trying to answer these questions by comparing and contrasting the significances of both. Kantian rationalism suggests a compatibility in the form of the ``religion within the limits of reason alone`` by postulating an almighty moral legislator who should assure us the achievement of the highest moral good. But Kierkegaard regards this way of combining of religion and moral as the shameful surrender of Christian belief to human understanding. As a result, Kierkegaardian religiosity and Kantian morality are incompatible with each other as long as each of them does not give up its own religious or rationalistic radicalism. To clarify this absolute difference between both, I will examine Kierkegaardian conception of the Christian paradox and the superiority of religious existence over ethical one, and then outline Kantian conception of the ``religion within the limits of reason alone.`` Hereby it will be proved that Kierkegaard and Kant are the philosophical-historical examples which show the fundamental difference between belief and reason, religiosity and morality.