Potassium (K), calcium (Ca), and magnesium (Mg) are important nutrients for the pummelo’s growth and productivity. However, these nutrients are strongly antagonistic to each other. This study aims to examine the effects of different K, Ca, and Mg ratios in soil on nutrient uptake of pummelo plant. Soil samples were collected under pummelo canopies at a depth of 0 cm to 20 cm. Leaf samples of 3 to 5 month old were obtained from the same trees. The soil’s chemical properties and nutrient concentrations in the leaves were determined. The results showed that the P uptake was inhibited by a high Ca concentration in soil. High K/Mg ratio in soil (0.52 ± 0.27) positively affected on K uptake. Low K/Mg ratios in soil (0.42 ± 0.20) negatively affected on K uptake, although exchangeable K in soil was much higher than optimum ranges. The K/Ca mole ratio in the leaves was higher than that in the soil; therefore, the uptake of K was better than that of Ca, despite the lower concentration of K in the soil. Moreover, the uptake of K was better than that of Mg, because the K/Mg ratio in the leaves higher than that in the soil. Low exchangeable Ca negatively affected on Ca uptake, although Ca/Mg mole ratio in soil was high (2.77 ± 1.18).