This paper presents the results of the development of an equipment for measuring pupil size variation. A Pupillometer has been developed in order to detect the pupil’s variation in time in a non-invasive way. The output signal of the equipment expresses the pupil’s features variation in time (area, perimeter, vertical diameter, horizontal diameter). The Autonomic Nervous System (ANS) is divided into the Sympathetic and Parasympathetic components and theoretically they are always competing with each other as a two oscillator model. The aim of this project is to identify these components and their frequency bands. With the present results we show that the signal from the pupil’s variation has two major frequency bands, the first being the 0-1 Hz band (LF - Low Frequency) and the second being 1-2Hz band (HF - High Frequency). From the literature we know that the Sympathetic Nervous System (SNS) behaves in a lower frequency than the Parasympathetic (PSNS) one. This means that SNS oscillates in the LF band and PSNS oscillates in the HF band.