Two field experiments of rice were conducted to study the effects of potassium (K) fertilizer on rice yield, economic profit, K utilization rate and on the field K balance in hilly ecoregion of southeastern Hubei and Jianghan Plain ecoregion. The results showed that K fertilizer increased obviously rice yield and economic profits in the two ecoregions, rice yield in Jianghan Plain increased with the increase of K utilization rate and the highest increased yield was 3 007 kg/hm2 with net economic profit of 4 136 Yuan/ hm2 under 187.5 kg/hm2 application of K2O. Rice yield in southeastern Hubei increased significantly with K fertilization but no significant differences among different rates of K fertilization, 150 kg/hm2 application of K2O obtained the highest increased rice yield (1 495 kg/hm2) with net economic profit (1 852Yuan/ hm2). The average K utilization rate in Jianghan Plain was 74.6%, which was lower than that (98.7%) in hilly ecoregion of southeastern Hubei. The result also found the negative K balances in the two ecoregions after rice growing, which could be relieved by K fertilizer application.