P. olivaceus may refer to:
Panaeolus olivaceus, a mushroom species Paralichthys olivaceus, the olive flounder, a flatfish species Phylloscopus olivaceus, the Philippine leaf warbler, a bird species Picumnus olivaceus, the olivaceous piculet, a bird species Prionochilus olivaceus, the olive-backed flowerpecker, a bird species Pristimantis olivaceus, a frog species Psophodes olivaceus, the eastern whipbird, a bird species