Two unprecedented isomeric secondary metabolites named vibralactones Z₅ (1a) and Z₆ (1b), in addition to eleven known compounds (2-12), were isolated from solid-state rice culture medium of Bondarzewia mesenterica (Bondarzewiaceae). Chemical structures of the isolated compounds were established via spectral analyses. The new lactone derivatives were weakly active against Staphylococcus aureus without any significant cytotoxicity, while the molecules containing an aldehyde functionality showed significant antimicrobial and cytotoxic effects. For instance, erinacine P (7) and (+)-isovelleral (8) and erinacine P (7) were cytotoxic against all tested cell lines at IC₅₀ values in the ranges of 3.5-14.2 and 2.8-30.2 μM, respectively. In addition, they revealed moderate antimicrobial activity with the lowest minimum inhibitory concentration (MIC) values recorded against Mucor hiemalis (8.3 μg/mL), Pichia anomala, and Rhodotorula glutinis at 16.6 μg/mL.