In order to obtain high yield components and good competitive indices of fennel and onion, different intercropping systems (sole crop of each components, 1:1, 1:2, 2:1 and 2:2 of fennel: onion, respectively) under different potassium fertilizer levels (0.0, 24 and 48 kg K2O/feddan) were used. A field experiment was carried out at Experimental Farm (Ghazala Farm), Faculty of Agriculture, Zagazig University, Egypt during the consecutive seasons of 2019/2020 and 2020/2021. The achieved results revealed that, intercropping systems significantly decreased fruit and bulb yield per feddan of fennel and onion, respectively, compared to sole crop of each one. Data obtained clearly that, rate of 24 as well as 48 kg of potassium level/ feddan gave increased of yield components of each fennel or onion plants. Furthermore, aggressivity and competitive ratio values indicated that fennel component were the dominant, whereas onion was the dominated one in different intercropping systems. The highest value of land utilization efficiency percentage (128.91 and 137.67 as well as 136.86 and 135.10) were obtained when fennel intercropped with onion at 2: 1 as well as 2: 2 systems under fertilization level of 24 K2O/feddan in 1st and 2nd seasons, respectively. Therefore, the intercropping systems of 2:1 and 2: 2 raised yield advantage over the sole crop per unit area as revealed by the highest total land equivalent ratio (LER), area time equivalent ratio (ATER) and land utilization efficiency (LUE%).