Abstract: Availability of azolla-potassium for rice was studied with radioactive tracer. The results of experiment showed that azolla released 66% potassium in the first seven days after azolla pressed into soil, The utilization rate of azolla-potassium for rice could reach 40%, which was a little higher than the efficiency of the same amount of potassium in chemical fertilizer. It was thought whether in potential capacity of absorbent potassium or in the capability of supplying potassium azolla was an important resourse of living things supplying potassium.