Twelve new lanostane triterpenoids, sterenoids A-L (1-12) have been isolated from fruiting bodies of the basidiomycete Stereum sp. Compounds 1-12 are rare 14(13→︀12)abeo-lanostane triterpenoids featuring remarkable 13R configurations that discriminate from the previously covered counterparts. Their structures and absolute configurations are assigned on the basis of in-depth one- and two-dimensional NMR spectroscopic analysis, as well as unbiased quantum chemical NMR and electronic CD calculations. All isolates are evaluated for their in vitro cytotoxicity against five human tumor cell lines. Compound 5 exhibits potent cytotoxic activities against tumor cell lines HL-60 and SMMC-7721 with IC50 values of 4.7 and 7.6 μM, respectively.