Air quality monitoring is traditionally performed using fixed monitoring stations in controlled environments. The instrumentation used in these stations, is often complex, bulky, very expensive, and it requires frequent maintenance works. Recently, the advancements in the field of digital technology and network communication made it possible to imagine a new paradigm of monitoring based on low-cost gas sensors. This latter is a very emerging technological area that offers considerable practical application. In this work, the performance evaluation of a low-cost O3 outdoor gas sensor was analysed by means of a comparative infield test. At this scope, we collected data in a strongly urbanized coastal zone, using both a commercial O3 monitoring station and a prototype station based on low-cost metaloxidesemiconductors (MOX) gas sensors. Finally, the performance and reliability of the low-cost prototype sensor versus the commercial one was evaluated through direct comparison between the acquired data.