Bioassay-guided fractionation of the chloroform extract of bulbs of the orchid P. michuacana was used to determine the chemical identity of bioactive constituents. The use of DPPH assay led to the isolation of two new lanostane triterpenoids 3a-acetoxy, 24-hydroxy-24-methyl-5a-lanosta-9(11),25-diene (1) and 3a-acetoxy, 24-hydroxy-24-methyl-5a-lanosta-9(11)ene (2), a new stilbene a-a'-dihydro,3',5',2-trimethoxy-3-hydroxy4-acetyl-4'-isopentenylstilbene (3), the phenanthrene 4,6,7-trihydroxy-2-methoxy-8-(methylbut-2enyl)phenanthrene-1,1'-4',6',7'-trihydroxy-2'-methoxy-8'-(methylbut-2'-enyl)phenanthrene (4), one new abietane-type diterpene 12-hydroxy-3{,7{,18a-triacetoxy-8,11,13-abietatriene (5), together with gigantol (6), a known compound. The compounds were identified by spectral analysis and comparison with spectroscopic data reported in the literature. Compounds 3, 4, 5, and 6 showed DPPH and ABTS radical-scavenging and anti-lipid peroxidation activities, but none of the isolated triterpenes showed promising antioxidant activity.