In this study, we developed an instrument-free visual pH determination method using a wedge-shaped microspace with pH-dependent swelling hydrogel particles. This method of pH measurement is achieved by utilizing the property of the hydrogel to swell with increasing pH and the wedge-shaped microspace in a 3D structure. Hydrogel particle formation using a microdroplet-forming chip and an ultraviolet LED enabled the fabrication of spherical pH-responsive hydrogel particles. Microchips with a wedge-shaped microspace of 500–3500 µm could be fabricated using the structures created by a photo-engineered 3D printer as templates. Evaluation of the method using a pH standard demonstrated that the settling distance of the particles decreased with increasing pH, and that the sensitivity and pH resolution were estimated to be 2.94 mm/pH and 0.2 pH, respectively. These results indicated that the method has the potential to visually measure pH. Furthermore, the developed method was applied to the determination of creatinine using creatinine deiminase. The method is readily applicable to biosensing technologies based on pH transduction, making it useful for on-site analysis in a wide range of fields, including medicine, environment, and food. Moreover, it can be adapted to microfluidic analysis for visual quantification using device-free micrototal analysis systems or lab-on-a-chip.