A method for predicting long-term efficacy of a VEGF inhibitor of the present invention includes determining whether or not an RAS gene-derived nucleic acid or an RAS protein is present in a blood sample collected from a subject, determines whether the RAS gene-derived nucleic acid in the blood sample is a wild type or a mutant or whether the RAS protein in the blood sample is a wild type or a mutant, determining that an antitumor effect resulting from the VEGF inhibitor is highly likely to last for a long period of time in the subject in a case where a wild-type RAS gene-derived nucleic acid or a wild-type RAS protein is detected in the blood sample and a mutant RAS gene-derived nucleic acid or a mutant RAS protein is not detected in the blood sample.