Two new ylangene-type sesquiterpenoids, postinins A (1) and B (2), were isolated from cultures of the fungus Postia sp. Structures 1 and 2 were elucidated on the basis of extensive spectroscopic analysis. The bioactivity evaluation showed that both compounds had significant inhibitory activities against protein tyrosine phosphatase 1B, and SH2-containing cytoplasmic tyrosine phosphatase-1 and -2 with IC₅₀ values of 1.6-6.2 μg/ml.