Background: Group 2 innate lymphoid cells (ILC2s) are a newly identified cell population with the potent capability to produce Th2-type cytokines in a non-antigen specific manner. Previous study demonstrated that enhanced circulating ILC2s in cat-allergic patient after experimental allergen challenge, whereas the effects of natural allergen exposure on peripheral ILC2s are still unclear. We therefore examined the variations in circulating ILC2s among asthmatic patients sensitized to different allergens in-and outside-pollen season. Methods: 10 patients sensitized to mugwort, 10 patients sensitized to house dust mites (HDM) and 12 healthy controls were recruited into this study. Blood samples were collected from the patients in-and outside-pollens season, 2-3 months apart. ILC2s (Lin-CD127+ CRTH2+) were enumerated by flow cytometry, as well as intracellular IL-5 and IL-13 expression. The levels of IL-5 and IL-13 in supernatants of Lineage-and Lineage+ cells stimulated with IL-25 and/or IL-33 in the presence of IL-2 were measured using a Milliplex human cytokine array kit. Results: An obvious seasonal increases in percentages of total and IL-13+ ILC2s were observed in patients with mugwort sensitization during natural pollen exposure, however, the percentages of peripheral ILC2s in HDM-allergic patients were not affected significantly. A positive correlation between FeNO and IL-13+ ILC2s was found in patients sensitized to mugwort. A mixture of IL-33 and IL-25 induced a significant production of IL-13 and IL-5 from Lineage(-) cells of both mugwort-allergic and HDM-allergic asthmatics. Stimulation with IL-33 alone induced a significantly greater quantity of IL-13 by Lineage-cells from mugwort-allergic asthmatic compared with that from HDM-allergic asthmatics, whereas IL-25 induced a significantly greater amount of IL-5 by the Lineage-cells from mugwort-allergic asthmatic compared with that from HDM-allergic asthmatics. Conclusion: Within pollen season the frequencies and function profiles of circulating ILC2s among asthmatic children are altered dynamically, which may be closely related to the sensitized type of allergens.