A new triterpenoid and 18 analogues were isolated from the water extract of Ganoderma lucidum by column chromatographic techniques, including silica gel, ODS, Sephadex LH-20, and HPLC. The new compound was elucidated as 2β-acetoxy-3β,25-dihydroxy-7,11,15-trioxo-lanost-8-en-26-oic acid on the basis of analyses of extensive spectroscopic data and its physicochemical properties. Comparison of NMR data with those reported in literature, the known analogues were determined as ganoderic acid H (2), 12β-acetoxy-3β,7β-dihydroxy-11,15,23-trioxo-lanost-8,16-dien-26-oic acid (3), ganoderenic acid D (4),ganoderic acid C1 (5),ganoderic acid G (6),3β,7β-dihydroxy-11,15,23-trioxo-lanost-8,16-dien-26-oic acid (7),ganoderic acid B (8),ganoderic acid C6 (9),3β,15α-dihydroxy-7,11,23-trioxo-lanost-8,16-dien-26-oic acid (10),ganoderic acid A (11),ganolucidic acid A (12),lucidenic acid E2 (13),lucidenic acid N (14),lucidenic acid P (15), lucidenic acid B (16),lucidenic acid A (17),lucidenic acid C (18),and lucidenic acid L (19), respectively. Compound 1 is new compound and compounds 2-19 have been reported from G. lucidum. The present study enriches the knowledge of the chemical constituent of G. lucidum and completes chemical investigation of water decoction that is traditional use of G. lucidum.