Two phenanthrenes were isolated from the aerial part of Dendrobium nobile Lindl. and their structures were identified to be 4,7-dihydroxy-2-methoxy-9,10-dihydrophenanthrene (1) and denbinobin (2), among which the former has been first isolated from this plant. These two compounds were found to be cytotoxic against A549 (human lung carcinoma), SK-OV-3 (human ovary adenocarcinoma), and HL-60 (human promyelocytic leukemia) cell lines. Compound 1 also showed antitumor activity on the life span of ICR mice intraperitoneally implanted with 1 x 10(6) cells of sarcoma 180.