This work aims to investigate to what the construction of fantasy in analysis refers, with references from Freud and Lacan. The concept of construction, a psychoanalysi s techinique different from interpretation, indicates a work done in analysis from what is forgotten in the history of the patient, the limit of remembrance. Faced with the impossible to interpret, one constructs, according to Freud, a scene that relates to the subject s primary fantasy. Lacan aproaches this construction in terms of fundamental fantasy. According to him, the construction of fantasy is the construction of a formula that governs the relationship between subject and object, a relationship that finds its basis in the position that takes the subject as an object of desire of the Other. The consideration of the construction of fantasy in the course of an analysis is especially important in psychonalysis with children, in which increasingly appear children with difficulties to separate from the object s position in the maternal fantasy.