This study describes the extraction and characterization of a novel inhibitor against ${eta}-hydroxy-{eta}-methyl$ glutaryl (HMG) Coenzyme A (CoA) reductase from the mushroom Pholiota adiposa. Methanol extracts of P. adiposa PAD-022 fruiting body showed the highest HMG-CoA reductase-inhibitory activity of 55.8%. The HMG-CoA reductase-inhibitor, P. adiposa PAD-022, was maximally extracted when its fruiting body was treated with methanol at $30^{circ}C$ for 12h. The HMG-CoA reductase-inhibitor was obtained by systematic solvent extraction methods followed by gel column chromatography, and RP-HPLC. The purified product was found to possess an activity of $IC_{50}$ $6.8{mu}g$ and a yield of 1.8%. The molecular weight of purified HMG-CoA reductase-inhibitor was deduced to be 412.7 Da. The inhibitor was identified as stigmasterol $(C_{29}H_{48}O)$ by serial instrumental analyses, including LC-Mass, NMR, FT-IR, and UV spectrometry.