Interactions between invasive plants and soil microorganisms play a key role in the invasion process. Exotic plants often produce allelochemicals that inhibit the growth of native plants by inducing changes in the physical and chemical properties of the soil, as well as to the structure of the soil microbial community. Chenopodium ambrosioides, an annual or short-lived perennial herb within the family Chenopodiaceae native to Central and South America, poses a threat to ecosystem structure and function in China. C. ambrosioides is rich in volatile oils, which are released into soils via root exudation and plant decomposition. Previous studies investigating the invasion mechanisms of C. ambrosioides focused primarily on its impacts on the growth of native plants and neglected its potential influences on soil microbial structure. Here, we used the greenhouse flask method to study the effects of volatile oils produced by C. ambrosioides on soil microbial diversity and extracellular enzyme activities. The results indicated that volatile oils deriving from C. ambrosioides inhibited the activity of soil urease, acid phosphatase, invertase and nitrate reductase (P<0.05), and high doses of these volatile oils significantly enhanced the activity of catalase (P<0.05). Moreover, the volatile oils had a strong influence on soil enzyme activities during the early stages of treatment, but this effect diminished considerably over time. Bacterial abundance was significantly higher in treatment groups receiving high doses (20 μL and 50 μL) of volatile oils than in the control groups (P<0.05) after 16 days of treatment, indicating that the volatile oils greatly influenced soil microorganism diversity; for instance, Actinomycetes were abundant when exposed to only low doses of volatile oils, but their populations declined at higher doses. Both Shannon-Wiener and Margalef indices indicated that bacterial and fungal diversity increased with increasing volatile-oil dose and treatment time. In conclusion, volatile oils produced by C. ambrosioides altered the microbial community structure and extracellular enzyme activities in soils, and increased soil microbial diversity.