Tightening environmental legislation is driving the chemical industries to develop efficient solid acid catalysts to replace conventional mineral acids. Polystyrene sulphonic acid resins, as some of the most important solid acid catalysts, have been widely studied. However, the influence of the morphology on their acid strength--closely related to the catalytic activity--has seldom been reported. Herein, we demonstrate that the acid strength of polystyrene sulphonic acid resins can be adjusted through their reversible morphology transformation from aggregated to swelling state, mainly driven by the formation and breakage of hydrogen bond interactions among adjacent sulphonic acid groups within the confined nanospace of hollow silica nanospheres. The hybrid solid acid catalyst demonstrates high activity and selectivity in a series of important acid-catalysed reactions. This may offer an efficient strategy to fabricate hybrid solid acid catalysts for green chemical processes.