The aim of the study was to investigate the dissolution kinetics of ulexite in borax pentahydrate solutions saturated with carbon dioxide in a batch reactor. Reaction temperature, stirring speed, CO2 flow rate, solid/liquid ratio and ulexite particle size were selected as parameters on the dissolution rate of ulexite. The experimental results were successfully correlated by linear regression using Statistica Package Program. Dissolution curves were evaluated in order to test shrinking core models for solid. fluid systems. It was observed that the increase in the reaction temperature and decrease in the solid/liquid ratio causes an increase in the dissolution rate of ulexite. The dissolution extent is not affected by the stirring speed rate in experimental conditions. The activation energy was found to be 42.5 kJ/mol. The leaching of ulexite that was controlled by the chemical reaction was also supported with the relationship between the reaction rate constant and the particle radius. The rate expression associated with the dissolution rate of ulexite depending on the parameters chosen may be summarized as follows: 1-(1-X)^(1/3)=9.725×10^(5)·D^(-0.8)·(S/L)^(-0.6)·W^(0.1)·e^(-42,525/RT)·t.