Background. A close relationship between outcome in patients with early-onset asthma and atopy has been reported. Allergic sensitization in early life seems to be an important risk factor for subsequent persistent asthma during childhood and adulthood. It might be valuable to evaluate atopy in patients with early-onset asthma in order to predict prognosis and take early intervention. Methods: Clinical data of 62 asthmatic children under 4 years of age were collected. The atopy status of each patient was determined by both personal allergic history (eczema and/or allergic rhinitis) and specific diagnosis of allergens (screening tests of fx5E, mx2 and Phadiatop conducted by fluoroenzyme-immunometric assay using the UniCAP100 system). The total serum IgE level was also measured. Logistic regression was used to analyze the effect of clinical characteristics on allergic sensitization. Results: There were 74.2% children who reported personal history of atopy and 33.9% reported parents' history of atopy based on the clinical data. The positive rates of fx5E, mx2, and Phadiatop were 40.3%, 14.5%, and 14.5% respectively. The total rate of allergic sensitization was 46.8% and the rate of sensitization to inhalant allergens was 24.2%. The allergic history of parent(s), the sensitization to food allergen, the age of first wheezing attack, and the total serum IgE level were main factors influencing sensitization to inhalant allergens. Conclusion: The asthmatic history of parent(s), the sensitization to food allergens, the age of first wheezing attack above 2 years and the significantly higher total serum IgE level may increase the possibility of sensitization to inhalant allergens in asthmatic children under 4 years of age.