Two skeletally novel tetracyclic diterpenoids, psathyrins A (<b>1</b>) and B (<b>2</b>), have been characterized from cultures of the basidiomycete <i>Psathyrella candolleana</i>. Their structures including absolute configurations were established by means of spectroscopic methods, as well as ECD calculations. They possess a novel 5/5/4/6-fuesd ring system, for which the biosynthetic pathway is proposed. Compounds <b>1</b> and <b>2</b> inhibited the growth of <i>Staphylococcus aureus</i> and <i>Salmonella enterica</i>.