We report a 52-year-old female patient with cholangiocarcinoma who developed severe bone marrow suppression after taking Selaginella doederleinii as an alternative anticancer treatment. She developed severe pancytopenia with initial presentations of skin ecchymosis, itching, and gum bleeding 2 weeks after taking Selaginella doederleinii daily. Bone marrow smear and biopsy showed severe hypocellularity with no malignant cell infiltration. Approximately 1 week after stopping Selaginella doederleinii, her hemogram returned to previous levels. Selaginella doederleinii, a popular anticancer herb, may contain an as yet unidentified substance that contributes to reversible bone marrow suppression.