Objective To determine the leucocyte profile and cytokine concentrations in the peripheral blood of children with an acute asthma exacerbation (AAE). Methods This descriptive, cross-sectional study enrolled paediatric patients admitted to hospital for AAE. The severity of AAE was assessed using the paediatric asthma score (PAS). Peripheral blood samples were collected for automatic quantification of white blood cell counts, CD3+, CD4+, and CD8+ T cells populations by flow cytometry and cytokine concentrations by flow cytometry-assisted immunoassay. Results A total of 127 children with AAE and 30 healthy control subjects were included in the study. The proportion of paediatric patients with decreased CD3+, CD4+ and CD8+ T cells was significantly higher in those with severe AAE compared with those with mild-to-moderate AAE. The concentrations of interleukin (IL)-2, IL-8, IL-12, and IL-4 in paediatric patients with rhinovirus infection were significantly higher than in those without rhinovirus infection. IL-2, IL-4, IL-6, TNF-alpha and GM-CSF concentrations during AAE were significantly lower than control. IL-5 and IL-13 concentrations during AAE were significantly higher than control. Conclusions The decrease of CD3+, CD4+, CD8+ T cells and IL-2, IL-4, IL-6, TNF-alpha, and GM-CSF combined with the increase of IL-5 and IL-13, were associated with AAE in children with asthma.