Essential oils of four Citrus species, Citrus aurantifolia, C. limon, C. paradisi and C. sinensis, were extracted from fruit peels by hydrodistillation. The chemical composition of the isolated oils was analyzed by gas chromatography/mass spectrometry (GC-MS). Effect of the isolated essential oils on seed germination and seedling growth of Silybum marianum was evaluated. The essential oils were also tested for their molluscicidal and insecticidal activities against the adults of Theba pisana snails and the fourth instar larvae of Spodoptera littoralis.  Chemical analysis showed that dl-Limonene was the major component in the four essential oils and represented 40.19, 56.30, 74.29 and 89.23% of C. aurantifolia, C. limon, C. paradisi and C. sinensis, respectively. In general, the four oils were characterized to be rich in monoterpene hydrocarbons and oxygenated monoterpenes. Allelopathic experiment on S. marianum revealed that the tested oils reduced the germination percentages at all of the tested concentrations. The oil of C. aurantifolia caused the highest germination reduction at concentration of 10 μL/ Petri dish where 26.7 % of seeds were germinated. The oil of C. sinensis was the most potent inhibitor for root and shoot growth of S. marianum with EC₅₀ values of 2.5 and 6.97 μL/Petri dish, respectively. The tested oils were more effective in reducing the growth of roots than shoots, except for C. paradise which stimulated the root growth. On the other hand, the tested oils showed strong fumigant toxicity againstthe adults of T. pisana snail with C. sinensis oil (LC₅₀ = 14.2 μL/L) being the most potent one. Also, the tested oils possessed a remarkable toxic effect against the fourth instar larvae of S. littoralis and the oils of C. aurantifolia and C. sinensis had the highest toxic effect with LC₅₀ values of 6.84 and 6.88 μL/L, respectively. The findings of the present study suggest that the essential oils have a potential to be used for pest control.