In present study, the dissolution kinetics of ulexite in phosphoric acid was-studied. The effects on the dissolution rate of particle size, temperature, acid concentration, solid-to-liquid ratio and stirring speed were experimentally investigated. It was determined that the dissolution rate increased with decreasing particle size and solid-to-liquid ratio and increasing reaction temperature. For acid concentrations up to 1 mol L-1, dissolution rate increased with increasing acid concentration. For higher acid concentrations, the dissolution rate was decreased as acid concentration increased. No effect of stirring speed on the dissolution rate was observed. The dissolution kinetics of ulexite was examined taking into consideration the heterogeneous and homogeneous reaction models. The tests carried out by graphical and statistical methods were showed that the following models with chemical reaction control for two different concentration levels was best fitted to the experimental data.