Potassium fixation was studied with < minerals and 10 soil samples under 5 potassium concentrations at room temperature and 60℃. After equilibrium of samples with different K levels in solution, the K fixed that was not extracted by 1 N neutral NH₄OAc is considered as fixed K of slowly available form, and the K fixed that was not extracted by 1 N boiling HNO₃ is considered as fixed K of mare slowly available form. The results obtained are summerized as follows: 1 Rate of potassium fixation for all samples was significantly correlated with the increase of K concentrations; the fixed K of slowly available form was much more than the fixed K of more slowly available form. 2. The lowest rate of fixed h of slowly available form was found in kaolinite, next in montmorillotaite, the highest in vermiculite, then in illite. Biotite and muscovite were between montmorillonite and illite.