To elucidate the mineral cycles of potassium in a dynamic grassland ecosystem in a steady state condition, this investigation was cunducted along the northwest side on Mt. Kwanak. The exper-imental results may he summarized on communities of Z. japonica and M. sinensis as follows. As compared with some pronerties of the surface soils among two semi-natural grasslands, the levels of exchangeahle potassium were high in M. sinensis and low in Z. japonica. Contents of potassium for the litters of Z. japonica and M. sinensis were 1.69% and 2.51%, re-spectively. The annual production of potassium was 1.32 g /m$m^2$ in the Z. japonica grassland and 3. 08 g /m$m^2$in the M. sinensis grassland. For a case of steady production and release, the ratio of annual min- eral production to the amount accumulated on top of the mineral soil in a steady state provides estimates of the release constant k. The models of the release, accumulation and annual cycle of potassium in a grassland ecosystem are determined by the equation (1) to (3), respectively (Table 3). Since it requires a period of about each 0.693 /r, 3 /r and 5 /r years for the release and accumu-lation of 50, 95 and 99% of its steady-state level, the estimates for potassium in a dynamic grass-land ecosystem of Mt. Kwanak were 1.5, 6.6 and 11.0 years in the Z. japonica grassland, and were 2.7, 11.9 and 19.8 years in the M. sinensis grassland. The amounts of annual cycles for potassium in a grassland ecosystem under the steady-state conditions were 1.32 g /m$^2$ in the Z. japonica grassland and 3.08 g /$m^2$ in the M. sinensis grassland. Key words : ZQvsia japonica Ahscanthus sinensis, Mt. Kwanak, Potassium cycles.