The current work was carried out during the two growing seasons of 2016/2017 and 2017/2018 at the Experimental Station of the Environmental Studies and Research Institute, University of Sadat City, Sadat City, Menofia Governorate, Egypt. It aimed to investigate the effect of applying potassium fertilizer at 90, 140 and 190 kg K2O/ha combined with spraying applications of seaweed extract for four times in a 15-day interval starting at 40 days after sowing at rates of 0.0, 1.5 and 3.0 ml/L on the yield, mineral contents and nutritional quality of quinoa grains cv. CICA. A split-plot design was used in three replicates. Results reported that by increasing the application of potassium from 90 to 190 kg K2O/ha, gradual increases in all studied parameters of quinoa grains occurred in the seasons of 2016-2017 and 2017-2018, except for class B grain and Mg and fiber contents. Potassium application at 190 kg K2O/ha gave the highest significant values of all determined parameters in comparison with treatment of 90 kg K2O/ha. In most cases, insignificant differences were detected between potassium fertilizer levels of 140 and 190 kg K2O/ha. Spraying seaweed extract at 3.0 ml/L resulted in superiority of all studied characters except class B grain and Mg and fiber contents, followed by 1.5 ml/L treatment with insignificant differences between them in most cases. There were significant differences among spraying seaweed treatments on Ca, Fe, Mn, protein and fiber contents in both seasons, N, P and K during the first season, and grain yield/plant, total grain yield/ha and Zn content during the second season. The interaction between potassium fertilization levels and spraying applications of seaweed extract had significantly different effects on all studied characters during both seasons, except for Mg percentage. It is evident that the application of potassium fertilization at 140 or 190 kg K2O/ha combined with the spraying of seaweed extract at 3.0 ml/L caused an apparent enhancement of the yield, mineral contents and nutritional quality of quinoa grains in comparison with the treatment of 0.0 ml/L (control) during the two experimental seasons.