Reaction of oxalic acid crystals with borax solution was experimentally investigated in a 1.5 L batch reactor at different operating conditions. The reaction was fast and took place very near to the surface of solid reactant. The dissolution process was found to be bulk diffusion controlled. A surface reaction model considering particle shrinkage was proposed for description of the process. Predicted fractional conversion of oxalic acid crystals were in good agreement with experimental values at different operating conditions. Conversion of oxalic acid crystals was significantly affected by the initial mean size of the solid reactant, while the temperature had the smallest effect. The activation energy of the dissolution process was determined as 12.89 kJ mol(-1). The proposed process can be used as an alternative way for boric acid production.