Effects of low molecular weight organic acids (LMWOA) on K⁺ adsorption kinetic characteristics of Red Soil and Yellow-cinnamon Soil were studied with the continuous flowing method to explore an optimal model for describing K⁺ adsorption kinetics. Results show that the red soils in all the LMWOA treatments, except in the treatment of 0.1 mmol L^-1 oxalic acid, adsorbed less K⁺ than it did in CK (soil without addition of LMWOA), and the yellow-cinnamon soils varied in K⁺ absorption significantly with K⁺ concentration. When K⁺concentration was 0.1 mmol L^-1, the yellow-cinnamon soils adsorbed less K⁺ than it did in CK, but when K⁺ concentration was raised up to 1.0 mmol L^-1, they adsorbed more than it did in CK. The K⁺ adsorption capacities of the two soils varied with the type of organic acid, showing an order of oxalic > citric > malic. The reaction velocity of K⁺ adsorption in the two soils was found to be in a good linear relationship with the natural logarithm of time “lnt” (r_0.05=0.754, r_0.01=0.874). The treatment of 1.0 mmol L^-1 K⁺ was higher in initial adsorption rate, but dropped faster in reaction velocity. In fitting the data of K⁺ adsorption in the red soil and yellow-cinnamon, the two-constant, exponential and Elovich equations were all quite effective, reaching the level of extreme significance, but the first order equation was not so good. The correlation coefficient of the two-constant equation was higher than that of the exponential equation and the Elovich equation, which rendered two-constant equation the best-suited model to describe K⁺ adsorption kinetics in the soils treated with organic acids. Under the effect of organic acids, K⁺ adsorption in the two soils was mainly influenced by soil charge.