Although specific IgE to the storage mite Acarus siro is often detected, there are no detailed studies on IgE reactivity to A. siro in Korea. This study was undertaken to investigate the cross-reactivity to the mite species Dermatophagoides pteronyssinus, Dermatophagoides farinae, Tyrophagus putrescentiae, and A. siro in Korean mite allergic patients. Specific IgE values were determined for the four mite species and a competitive inhibition test was performed for mite extracts using the ImmunoCAP system. The IgE value to D. farinae was the highest among the four mite species tested. There was a strong correlation in the IgE value between house dust mites (D. pteronyssinus and D. farinae) and between storage mites (A. siro and T. putrescentiae). IgE reactivity to A. siro was inhibited by D. farinae and T. putrescentiae extract. Dermatophagoides farinae extract was the strongest inhibitor of IgE binding to A. siro extract, indicating that IgE reactivity to A. siro extract is a cross-reaction caused by sensitization to D. farinae. Strong IgE reactive components were observed in D. farinae and T. putrescentiae extract by SDS-PAGE and IgE immunoblotting. However, no strong IgE-binding component was observed for A. siro. Dermatophagoides farinae is the main source of mite allergens that cause sensitization in Korea. Serum IgE from some of the house dust mite-sensitized patients showed positive responses to storage mite allergens by cross-reaction. Therefore, it is necessary to pay special attention to the diagnosis of mite allergies.