The separation efficiency of cesium (Cs(I)) and rubidium (Rb(I)) from a synthetic brine solution containing potassium (K(I)) was improved via a kinetics-controlled strategy. Specifically, 4-tert-butyl-2-(alpha-methylbenzyl) phenol (t-BAMBP) dodecane solution was partially saponified by NaOH solution first and then was directly used in extraction without adjusting the pH of the feed solution to exceed 13. Compared to the traditional process, much higher separation factors of Cs(I) and Rb(I) over K(I) (beta(Cs/K) = 1550.7, beta(Rb/K) = 45.2) were gained due to the enhanced kinetics differences during ion exchanges. In addition, the consumption of NaOH was reduced by 70-97%, and a large amount of strong alkaline wastewater was avoided because of the recydability of NaOH saponifying agent. For synthetic brine solution containing high concentration K(I), 99.1% Cs(I) and 86.5% Rb(I) were recovered after three-stage extraction. The novel process showed a bright prospect for the extraction of Cs(I) and Rb(I).