We studied a method of implementing an electrochemical sensor with high response speed using a film made of metal oxide nanoparticles. The optimal conditions for sensor production were estimated by calculating the sensor’s response when the bulk and surface resistances of the film changed. We also implemented a new manufacturing process to fabricate the sensor. To achieve high response speed, an ITO:CB film was produced by mixing ITO nanoparticles and carbon black (CB) powder. Depending on the CB content of the ITO:CB film, the response time of the sensor continued to decrease from 337 s (CB = 0 wt%) to 2 s (CB = 50 wt%). However, even in this case, a continuous decrease in response intensity was observed as well. Therefore, to ensure high response speed and appropriate response intensity, a new process of oxygen ashing the film surface was introduced. As a result, it was possible to secure high response intensity and high response speed at CB contents up to 30 wt%. On the basis of these results, we confirmed that CB mixing and surface oxygen ashing can improve both the response intensity and speed of sensors using metal oxide nanoparticle films.