A new process for recovering the potassium content from bittern is developed in this study. In the process, the potassium content of bittern is crystallized as potassium pentaborate octahydrate by the addition of sodium pentaborate. The equilibrium conditions of potassium pentaborate octahydrate crystallization are examined as functions of the amount and concentration of sodium pentaborate solution and temperature. It is found optimum crystallization conditions are at 15 degrees C by using a sodium pentaborate solution saturated at 25 degrees C. At these conditions about 65% of the potassium content can be easily recovered as potassium pentaborate octahydrate, which is easily converted into any desired potassium salt.