In this work, a novel type electrode based on RuO2 nanoparticles-modified vertically aligned carbon nanotubes (RuO2/MWCNTs) was prepared by magnetron sputtering deposition. This RuO2/MWCNTs electrode not only shows a high capacity nature, but also possesses a good response to the pH value. The pH sensor based on the RuO2/MWCNTs nanocomposite electrode exhibits some advantages over the conventional pH sensors. It shows good reproducibility, long-term storage stability (over 1 month) and linear response in the whole pH range (2–12) of Britton–Robinson (B–R) buffer solutions with near-Nernstian response (about −55mV/pH). The hysteretic widths of the nanocomposite electrode are 6.4mV, 5.1mV and 10.2mV in pH 7–4–7–10–7, pH 7–10–7–4–7 and pH 2–8–12–8–2 loop cycles, respectively. Moreover, the RuO2/MWCNTs electrode displays an excellent anti-interference property and fast response time (less than 40s). According to the electrochemical impedance measurements, the pH sensing properties of the RuO2/MWCNTs electrode were also discussed.