Introduction. The yellow passionfruit is consumed mainly as juice and is well accepted around the world. The nutritional state of the plant influences yield and fruit quality. We studied the particular effect of potassium nutrition on the quality of yellow passionfruit. Materials and methods. The experiments were conducted in a greenhouse at the Federal University of Viçosa, in Brazil, outlined in a randomized block design. The treatments were five concentrations of K [(1, 2, 4, 6 and 8) mmol·L–1] in a modified nutritive solution of Hoagland and Arnon. The experimental unit consisted of one plant in a 20-L pot containing washed sand. The plants were irrigated by a circulating hydroponic system. The nutrients were re-added to the solution based on its electric conductivity and on the K content in each solution. Results and discussion. The K supply increased yield and average fruit weight up to the concentration of (6.43 and 6.24) mmol·L–1, respectively, and linearly increased the number of seeds per fruit, thickness and relative water content of the pericarp and vitamin C content. The total titratable acid content increased according to a square equation, with the maximum point at 5.27 mmol K ·L–1. The pulp percentage, pH and total soluble solids content were not influenced by K doses. Conclusions. The increase in K supply promoted yield and fruit quality. At 90% of the maximum yield, the fruits had adequate quality traits.