Background: The prevalence of allergic diseases, particularly asthma and allergic rhinitis, has increased tremendously in Thailand and worldwide. House dust mite (HDM) is the major IgE sensitizer among allergic children and adults. We have developed local standardized mite allergen extracts, Siriraj Mite Allergen Vaccine (SMAV) from Dermatophagoides pteronyssinus (Dp) and Dermatophagoides farinae (Df) from our source materials which were highly purified (99%).Objective: To compare in-vivo allergenic potency of both SMAV Dp and Df with commercial standardized mite allergen vaccine by using skin prick testing in mite-sensitive individuals.Methods: This was a double-blind, randomized, self controlled study comparing SMAV and commercial standardized mite allergen vaccine (Dp and Df) by using skin prick testing in mitesensitive adult volunteers, 18 – 60 years of age.Results: The study was performed in 54 adult volunteers (19 males, mean age 26.6 + 5.5 years old) who had positive skin test to commercial Dp and Df. Seventeen of them had no allergic disease. The most common allergic disease among the volunteers was allergic rhinitis (21/37). Mean wheal diameter of SMAV Dp and commercial Dp at the concentration of10,000 and 5, 000 AU/ml were equivalent but at the concentration of 2,500 AU/ml wasinequivalent. Mean wheal diameter of SMAV Dp was significantly larger than commercialDp at concentration of 2,500 AU/ml (p < 0.05). Mean wheal diameter of SMAV Df and commercial Df at all 3 concentrations were equivalent. There was no systemic side effect in all subjects.Conclusion: The study demonstrated that in mite-sensitive adults, SPT using SMAV Dp(10,000 AU) and Df (10,000 AU) had equivalent allergenic potency to the commercial comparator without any systemic side effect.