The interference of weeds with the important oilseed crop of sunflower plants can cause great loss of crop yield of more than 58% and consequently oil yield. Therefore, weed management is important for sunflower growth and yield as well as oil seed yield. For this purpose, two pot experiments were carried out in the greenhouse of the National Research Centre, Dokki, Giza, Egypt for further investigation of allelopathic activity of Eucalyptus citriodora as leaf powder against the perennial weed purple nutsedge (Cyperus rotundus) associated sunflower plant (Helianthus annus). In these experiments, E. citriodora leaf powder was applied in the soil at rates of 5, 10, 20, 30 and 40g/pot in the two successive summer seasons of 2023 and 2024. The results indicated inhibition in all growth parameters of P. nutsedge (foliage and underground organs) as well as their fresh and dry weights. The reduction increased with increasing concentration. The inhibition in P. nutsedge growth characters was accompanied by an increase in sunflower growth and consequently yield that was represented by head diameter, dry weight of head, weight of seeds/head and weight of 100 seeds especially with 30g/pot. The results suggested the ability to use E. citriodora leaf powder as a natural herbicide for controlling P. nutsedge.