Three new lanostante-type triterpene aldehydes, named lucialdehydes A—C (1—3), were isolated from the fruiting bodies of Ganoderma lucidum, together with ganodermanonol (4), ganodermadiol (5), ganodermanondiol (6), ganodermanontriol (7), ganoderic acid A (8), ganoderic acid B8 (9), and ganoderic acid C1 (10). The structures of the new triterpenes were determined as (24E)-3β-hydroxy-5α-lanosta-7,9(11),24-trien-26-al (1), (24E)-3,7-dioxo-5α-lanosta-8,24-dien-26-al (2), and (24E)-3β-hydroxy-7-oxo-5α-lanosta-8,24-dien-26-al (3), respectively, by spectroscopic means. The cytotoxicity of the compounds isolated from the ganoderma mushroom was tested in vitro against Lewis lung carcinoma (LLC), T-47D, Sarcoma 180, and Meth-A tumor cell lines. Lucialdehydes B, C (2, 3), ganodermanonol (4) and ganodermanondiol (6) showed cytotoxic effects on tested tumor cells. Of the compounds, lucialdehyde C (3) exhibited the most potent cytotoxicity against LLC, T-47D, Sarcoma 180, and Meth-A tumor cells with ED₅₀ values of 10.7, 4.7, 7.1, and 3.8 μg/ml, respectively.