<p>Morphological modulation, structural, and functional variations of nanoparticles by altering reaction conditions, preparation methods, and precursor materials to produce nano combs, nano rings, nano helixes, nanobelts, nanowires, and nanocages have gained much attention in recent areas. The role of pH in governing the morphological transformations in ZnO nanoparticles represents a critical yet insufficiently explored aspect of research. ZnO is an inorganic compound with excellent chemical, electrical, and thermal stabilities, and has potential for research due to its nano-sized particles, wide bandgap, enhanced specific surface area, and surface reactivity. Surface groups undergo protonation or deprotonation by the change in hydrophilicity of the nanoparticles due to pH change that affects all the properties of NPs. In this review, the effect of pH on the morphological changes, chemical characteristics, and mechanistic insights of ZnO NPs is explored. Additionally, chemical, electrical, biomedical, optoelectronic, and antibacterial properties of ZnO NPs are studied by changing pH. In future, potential applications of pH-controlled morphology of ZnO NPs will be explored in catalysis, electronics, and biomedicine fields.</p>