Abstract: Pot experiment was conducted to study the response of Foeniculum vulgare plants to foliar application of nicotinamide. Data showed that, vegetative growth, essential oil percentage of different parts and yield significantly promoted by nicotinamide treatments up to 80 mg l‾1. Protein profile of the produced seeds and total carbohydrates were also influenced by the treatments. The most promising results with best yield and quality of fennel oil were obtained from plants treated with nicotinamide at 80 mg l‾1 at both cuttings; essential oil yield was maximal at 1st cut (0.14 ml oil/plant); it was high in the fruiting umbels (0.93 %), low in the leaves (0.33 %), but only traces occurred in the stems ( 0.07 %). GC/MS analysis revealed that the major components of all oil samples was trans-anethole (17.32, 20.96, 59.31 % in leaf, stem, fruiting umel, respectively). The other main components namely, limonene, γ- terpinene, estagole, fenchone, α- pinene and β- pinene. The volatile oil of leaf and stem contained high amount of anis-aldehyde. These components showed some qualitative and quantitative differences under the effect of nicotinamide treatments in different parts of fennel plants.