To develop a simple, low-cost and highly reliable testing method for mesothelioma, and a kit used for said testing method. The present invention provides a testing method for mesothelioma comprising a step in which the concentration of human periostin protein is measured in at least one type of sample from among samples of the blood or pleural fluid of a subject. The step in which the concentration of human periostin protein is measured may use an antibody directed against human periostin protein. The present invention further provides a kit for diagnosing mesothelioma, said kit including the antibody directed against human periostin protein. In one kit for diagnosing mesothelioma, the diagnosis of mesothelioma determines if a subject that may have mesothelioma has mesothelioma or is healthy. In another kit for diagnosing mesothelioma, the diagnosis of mesothelioma determines if a subject that may have mesothelioma has mesothelioma or has a respiratory illness other than mesothelioma.
