Pitaya stands out in the market for presenting exotic appearance species, high water content, vitamins and minerals, low calories, and bioactive compounds that makes it attractive for consumption However, the composition of this fruit may change according from the place of cultivation, orchard management and harvesting season. Regarding orchards management, variations have been observed in the fact that the pitaya species are considered rustic, able of tolerating adverse conditions of low availability of water and nutrients, and mainly because lack information on fertilization. Thus, the research was carried out to evaluated the potassium fertilization in the quality and in the centesimal composition in pitayas of the species Hylocereus undatus and Hylocereus polyrhizus. The evaluations were carried out during two harvests, in pitayas harvested mature from plants that received different fertilizations. The fruits of the pitaya species reach larger sizes and better flavor with the potassium fertilization. The fruits centesimal composition is altered with the management of the fertilization of the orchards. The fruits produced by plants with higher availability of potassium oxide (K2O) present higher contents of dry matter, fiber, ashes, carbohydrates and energetic value and lower moisture content, allowing conservation for longer if stored properly. The increase of these constituents in the fruit pulp is related to the function of potassium (K) in the enzyme’s activation, which are fundamental in the metabolic processes and the transport of photoassimilates, evidencing their role in improving fruit quality characteristics. Orchards that are fertilized with potassium produce fruits with better composition and final quality, increasing the acceptance by consumers, size classification and market prices.