The essential oils was obtained from leaf , stem and fruit of Xanthium italicum Moretti by steam distillation method , and their chemical composition was identified by GC-MS. Total 25, 23, and 27 compounds were identified from leaf , stem, and fruit oils, accounting for 90.625%, 93.041%and 89.866%of the total oil, respectively.The main components of leaf , stem and fruit oils were limonene(25.541%)and borneol(12.133%), limonene(62.85%),γ-elemene (23.38%), limonene (14.18%) and germa-crene B (16.279%).Amaranthus retroflexus L., a dicot plant, and Poa pratensis L., a monocot plant, which can be found to grow in the habitats that are invaded by X.italicum, were used as tested species to evaluate the allelopathic effects of the plant ′s volatile oils . Different amounts (20, 40 and 80 g/1.4 L) of fresh cut leaves, stems and fruits of X.italicum were placed in air tight containers to simulate its natural conditions to emit volatile oils into the environment , and petri dish bioassay method was used to evaluate the phyto-toxic activity of its essential oils at different concentrations (0.2 μL/mL, 0.5 μL/mL, 1μL/mL, 3μL/mL and 5 μL/mL).Results showed that the volatile oils of different plant parts exhibited significant allelopathic effect both under simulated natural conditions and in the petri dish bioassay , and leaf oil has the potential to be utilized as a natual herbicide .%采用水蒸气蒸馏法分别提取意大利苍耳（Xanthium italicum Moretti）叶、茎、果3个部位的挥发油，并通过GC-MS分析对其化学成分进行分析鉴定。在叶、茎、果挥发油中分别鉴定出25、23和27种化合物，分别占总成分的90.625％、93.041％和89.866％。其中，叶挥发油的主要成分是柠檬烯（25.541％）和龙脑（12.133％），茎挥发油的主要成分是柠檬烯（62.85％），而果挥发油的主要成分为γ－榄香烯（23.38％）、柠檬烯（14.18％）和吉玛烯 B （16.279％）。以意大利苍耳入侵生境中常见杂草反枝苋（ Amaranthus retroflexus L．，双子叶植物）和早熟禾（ Poa pratensis L．，单子叶植物）作为受试植物，在密闭容器中（容积为1.4 L）放入不同质量的叶、茎、果部位（20 g、40 g和80 g），检测其在模拟自然状态下产生的挥发物的化感作用；并采用培养皿法对不同浓度叶、茎、果挥发油（0.2μL／mL、0.5μL／mL、1μL／mL、3μL／mL和5μL／mL）的化感作用进行生测。结果显示：意大利苍耳各部位在自然挥发条件下以及其挥发油均表现出较强的化感作用，其叶挥发油在5μL／mL时可完全抑制两种受试植物种子的萌发，具有进一步开发为植物源除草剂的潜力。
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