Asthma is a common chronic inflammatory disease of the respiratory system. There are many kinds of biomarkers for asthma, but no specific ones have been found yet. Pulmonary surfactant-associated protein D (SP-D) is mainly located in the lung, but also mildly expressed in the other organ systems. SP-D plays important roles in body defense and immune surveillance, and is closely related to many pulmonary diseases. The protein is essentially involved in the development and progression of asthma, and can be used as a biomarker of bronchial asthma. In this we article reviewed the function of SP-D and its role as biomarker in asthma.