The mainly propose of this article was to develop theoretically a way to approach the topics of death and authenticity from the existential psychotherapy, starting off from the ontological, psychical and anthropological conditions of the human being, as well as from a theological indication, having as result the construction of a resolution as a proper way of self-care; also the foundation of an appropriate regional ontology for the approach of the authenticity and the possibility of the death in existential psychotherapy was made, through the clarification of many of the concepts used by this psychotherapeutic approach and considering some of the scientific levels contained within this ontology, mainly those referred to the psychotherapy process (psychotherapeutic strategies, approaching methods, therapist knowledges, stages of the psychotherapeutic process, characteristics of the existential psychotherapy) and to the psychopathology (defense mechanisms, constitution of the psychopathology)