The present study was conducted to investigate the effects of nitrogen (N) and potassium (K) on growth, yield, qualitative traits and antioxidant capacity of sweet fennel. The experiment was performed according to the factorial experiment based on randomized completely block design with three replications in two years (2017 and 2018). Treatments included four different levels of N (0, 50, 100 and 150 kg ha^-1, urea source) and K (0, 50, 100 and 150 kg ha^-1, potassium sulphate source). Results showed that application of N and K significantly increased plant height, leaf number, bulb diameter and length, and bulb fresh weight in both years. Increasing nitrogen concentration up to 100 kg ha^-1 increased the phenols and flavonoids contents and antioxidant activity, but application of 150 kg ha^-1 N caused a decrease in such parameters. Also, application of high level of K increased quality traits and antioxidant activity. Application of N and K fertilizers increased the content of them in bulb tissue in both years. According to the results, application of 150 kg ha^-1 K and 100 kg ha^-1 N could be recommended to improv grwth, bulb yield and antioxidant properties of sweet fennel.