We have developed a rolling circle amplification-procedure as a method to enhance signals of immunoassay (immuno-RCA) to detect one of the major food allergens, ovalbumin (OVA). Immuno-RCA in combination with a fluorescent dye and a circular DNA probe prepared by intramolecular ligation easily allowed the real-time detection of OVA, and could apparently detect signals from OVA with concentrations ranging from 10(-12) to 10(-7) g/mL. Therefore, sensitive and easily handled aspects of this method would contribute to an effective signal enhancement in immunoassay for food allergen detections.