In this work, we developed a surface-acoustic-wave (SAW)-based immunosensor for the monitoring of house dust mite (HDM) allergen, Dermatophagoides farinae group 2 (Der f 2). The SAW immunosensor was fabricated by modifying the sensor surface with a self-assembled monolayer of ORLA85 protein and immobilized capture antibodies (cAb) for Der f 2. Because of the pH-insensitive property of ORLA85, the sensor surface could be used for successive measurement and regeneration of the sensor surface. In experiments, first, the conditions for cAb immobilization on the sensor surface were optimized, and then the sensor properties were investigated. These revealed the limit of detection of the SAW immunosensor for Der f 2 to be 6.3 ng/mL and hence, the sensor’s high selectivity to Der f 2. Finally, the optimum pH for regeneration, at which the regeneration efficiency and sensor output were balanced, was investigated. It showed that the use of pH 4.0 HCl for regeneration allowed reproducible sensor outputs, and less damage to immobilized cAb; thus, longer sensor lifetime could be expected. The results allowed us to anticipate that the SAW immunosensor would be usable for sensitive, selective, and repeated measurement of Der f 2 with a longer lifetime, and it would be a promising sensor for HDM allergen monitoring.