The aim is to study the constitutional principle of presumption of innocence and its impact on the application of the fast-track procedure, in criminal matters. A qualitative methodology was used in this research, with the use of different methods, such as the analytical-synthetic method, as well as the historical-logical method, which were based on the exhaustive analysis of the principle of innocence and the fast-track procedure. The main technique used was an observation, since the Ecuadorian legal system was analyzed through a bibliographic-documentary approach in order to conclude that the application of the fast-track procedure is discussed and criticized due to its effectiveness in terms of procedural speed; the judicial system is considered vitiated by irregularities because it is insufficient to decongest the judicial system. When there is a suspension of any of the stages or procedures of the criminal process, a possible consequence is that an improper or erroneous judicial sentence is issued, violating the constitutional principles of due process.