In this study, we investigated the potential bioactivities of an ethanol extract of Hericium novae-zealandiae and four of its constituents, namely hericenone C, hericene B, ergosterol and ergosterol peroxide. The proliferation of three prostate cancer cell lines, namely DU145, LNCaP and PC3, was evaluated after treatment with the extract and constituents. It was found that both the ethanol extract and ergosterol peroxide possess anti-proliferative activities to the three prostate cancer cell lines. Ergosterol peroxide was considered likely to be one of the major compounds responsible for the anti-proliferative effect of the ethanol extract. Subsequently, the results of RT-qPCR assay showed two possible mechanisms for these anti-proliferative activities. One is apoptosis, supported by the up-regulation of CASP3, CASP8, CASP9, and an increase in the ratio of Bax/Bcl2. The other is anti-inflammation, indicated by the down-regulation of IL6 and up-regulation of IL24. The ethanol extract also exhibited antioxidant and AChE inhibitory (though weak) activities. However, none of the four compounds were found to account for these latter two activities. This is the first report of the bioactivities, and the corresponding active ingredients of lipophilic constituents from H. novae-zealandiae.