The existential Christology of Karl Rahner and of Therese of Calcutta is a research which objective is to present, in a comparative way, these both great mystics of the century without God (XX). This work is structured in five moments. First, It is presented the life of the German theologian which gives the tonic to the work. Then, the Christology of Karl Rahner from which we describe the proposal of a new Christological reflection for the present days, according to this theologian. At the same way, we explained the two Christological strands thought from the relation with the person of Jesus and treated by Karl Rahner which are both the descendant and the ascendant strand. In the third moment, It is presented the life of Therese of Calcutta – as we did with Rahner – from her spiritual experience. Then, the Christology of Mother Therese is described and oriented based on some theologians, who offer lights for the comprehension of this woman s thought who can and will be consider as a theologian. The last research moment is going to be structured in a comparative way. Rahner and Therese will be seen from the inconsequences of the called existential Christology, which affect the theological reflection. As a way of application, Pope Francis thought will be used, in order of realizing how much the reflections of the mystics can contribute with the renewal of theology and, as a consequence, the ecclesial life, in the present day. This manner, the existential Christology of Karl Rahner and of Therese of Calcutta will offer lights for the being a Christian in the XXI century.