The precautionary measure of preventive custody is an order issued when there are serious risks of the defendant fleeing, as defined by legal doctrine. However, in various legal systems, including the Ecuadorian, different criteria have been used to determine the deprivation of liberty. The overall objective of the research was to legally analyze the right to freedom of the defendant under the precautionary measure of preventive custody. The research was conducted from a quantitative perspective and framed within a documentary-bibliographic design. This involved the investigation, collection, and critical analysis of documentary and bibliographic references, based on a methodical, rigorous, and in-depth exploration of various documentary sources such as scientific research, articles, and peer-reviewed works, among others. It is concluded that preventive custody in the national criminal justice system is often applied solely in accordance with the law without verifying the fundamental rights recognized by the Constitution. Therefore, it should be applied with consideration to these rights. However, the main problem arises due to the lack of motivation when ordering such a measure.