Hydroxychloroquine (HCQ) has attracted the interest of scientists in the last two years, as its use in combating SARS-CoV-2 was being considered. Literature reports side effects linked to the use of HCQ [1], making it necessary to develop analysis methods for its monitoring. In this context, the use of nanomaterials [2], such as carbon nitride nanosheets (CNNS) in the modification of electrochemical sensors, provides an increase in the surface area and ease of electron transfers due to their properties [3]. In this study, a modified electrode with CNNS (CNNS/E) was developed for the selective determination of HCQ. The CNNS/E showed a great analytical performance (Fig. 1) for detection of HCQ, with the values obtained for limits of detection (LOD) and quantification (LOQ) of 0.16 nmol l-1 and 0.52 nmol l-1, respectively, being the lowest reported for electrodes. The method was successfully applied in the determination of HCQ in drugs and synthetic urine samples, with recovery values between 99.6% and 102.0%, and there was no significant variation (<10%) in the current intensity of the HCQ, when evaluated in the presence of concomitant species, highlighting the analytical importance of the developed sensor.