Biomass conversion is of great importance in the sustainable manufacturing of green chemicals, and it is well known as a viable way to deal with the shortage of fossil fuels and carbon emissions. Most biomass conversions are often governed by carbocation chemistry, which requires acidic active sites on the catalysts. Solid acid catalysts are considered as one of the most popular heterogeneous catalysts and are widely applied in biomass conversion. Among them, zirconia-based catalysts have received vast attentions as either a catalyst itself or a catalyst support owing to their desirable catalytic properties. This review presents bare zirconia and zirconia-based support catalysts for their wide applications in biomass conversion reactions. Various aspects of zirconia-based acid catalysts including synthesis methods, catalyst structures, acidities, reaction mechanisms, and applications are discussed. Thanks to their strong acidity, remarkable stability, versatility of modification, high catalytic performances, easy catalyst recovery and reusability, and environmentally friendliness, it is believed that zirconia and zirconia-based catalysts are one of the most practical and multifunctional solid acid catalysts in many acid-catalyzed biomass conversions.