<p>Strong polyelectrolyte brushes (SPBs) play an important role in enabling material surface functionalization due to their unique stimuli-responsive properties. Although the unexpected pH responsiveness of SPBs has been revealed in the past ten years, it is still unclear if the pH-responsive properties of SPBs are affected by the brush thickness. In this study, we employed the positively charged poly[2-(methacryloyloxy)ethyl] trimethylammonium chloride (PMETAC) and negatively charged sodium poly(styrenesulfonate) (NaPSS) brushes as model systems to explore the effect of thickness on the pH-responsive properties of SPBs. The results demonstrate that the pH-responsive properties of SPBs manifest different dependences on the brush thickness. Specifically, for both PMETAC and NaPSS brushes, the pH-responsive hydration and stiffness are influenced by the thickness, and the pH-responsive wettability and adhesion are almost unaffected by the thickness. This work not only provides a clear understanding of the relationship between the brush thickness and the pH responsiveness of SPBs, but also offers a new method to control the pH-responsive properties of SPBs.</p>