Abstract: The online measurement system of radioactive tracers in oil wells head, object of this invention, is characterized by the use of new technology to measure concentrations of tracer activity in real time, using a radiation detector NaI (TI), with features that make it possible to detect up to three different tracers and be able to operate in temperature conditions up to 150° C., which allows to be immersed in a container with fluid coming from the flow stream, achieving with this to increase the sensitivity of the measurements. This system of measurement in the head of production wells will allow having much more data of the tracer activity, avoiding having to transport the operational staff to production wells to carry out sampling test, with all the advantages that this represents.