The agricultural areas of the world face problems that create difficulties when producing food and the excessive use of fertilizers is generating a negative environmental impact. An alternative that appears as a solution to this problem is the use of nanofertilizers. Within nanofertilizers an area of opportunity is the application of macronutrients, which report an increase in absorption efficiency of 19% compared to conventional fertilizers. Potassium (K) is one of the three macronutrients most used in agriculture and its deficiency affects key processes in plant development, limiting crop production. However, the number of publications where K is used as a nanofertilizer is limited, despite this, products in this form are already on the market. Therefore, the aim of this research work was to study the effect of the foliar application of K nanofertilizer on biomass, yield, nitrogen assimilation and photosynthetic activity in green beans cv. ‘Strike’. K was applied in the form of a nanofertilizer in doses of 0, 50, 100 and 200 ppm. The biomass accumulation, yield, nitrate reductase enzyme activity, photosynthetic activity and photosynthetic pigments were evaluated. The dose of 100 ppm of K nanofertilizer obtained a higher accumulation of biomass, nitrate reductase activity, photosynthetic activity, SPAD values and total chlorophyll content. While the 200-ppm dose obtained a higher increase in yield. The results obtained suggest that the application of K nanofertilizers benefits the physiological development of plants. However, more studies are required to compare the application of nanofertilizers with traditional fertilizers.