An unusual clathrate-type meroterpenoid isoatlantinone A (1), two new steroids acrocalysterols E (2) and F (3), together with fifteen known compounds (4-18) were separated from a plant-associated fungus Penicillium fellutanum. Their structures and absolute configurations were established based on spectroscopic data (nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry), electronic circular dichroism and modified Mosher's method. Notably, compound 1 represents an unusual highly oxygenated meroterpenoid derivative with a unique caged bioxatetracyclo-[6.3.2.0