Despite the saline soils of Bangladesh having high potassium (K) availability, the acquisition of K by rice (Oryza sativa L.) is unsatisfactory. The study was designed to quantify the performance of rice yield components, macro-nutrient uptake, K+/Na+ ratio, and nutrient use efficiency under the influence of improved K fertilization in a salt-affected soil. The salt-tolerant Boro rice cultivar (BRRI-47) was tested with seven different K treatments (0, 20, 40, 60, 80, 100, and 120 kg K ha(-1)) with three replications followed by a complete randomized design (CRD). The results indicated that increasing K levels had a positive influence on most of the growth and yield parameters of rice except plant height, unfilled grain number, and 1000 grain weight. Application of 100 kg K ha(-1) raised the grain yield by 49% over control and 19.13% over the present national recommended dose (40 kg K ha(-1)). Straw yield increased by 42% in treatment K-120 and 36% in treatment K-100 over control, respectively. The K+/Na+ ratio in plants was observed to be higher when K was applied at higher rates. Additionally, the different K doses improved the nutrient (N, P, K, S) uptake and decreased the internal N and K use efficiencies of rice. It can be summarized that 100 kg ha(-1) K fertilization could be effective to improve rice production and nutrient uptake in coastal saline soil of Bangladesh while maintaining a high K+/Na+ ratio.