Four new cucurbitane-type triterpene sapogenins, compounds 1–4, together with other eight known compounds were isolated from the acid-hydrolyzed fruits extract of Momordica charantia L. Their chemical structures were established by NMR, mass spectrometry and X-ray crystallography. Compounds 1–7 and 9–12 were evaluated for their inhibitory activities toward protein tyrosine phosphatase 1B (PTP1B), a tyrosine phosphatase that has been implicated as a key target for therapy against type II diabetes. Compounds 1, 2, 4, 7 and 9 were shown inhibitory activities of 77%, 62%, 62% 60% and 68% against PTP1B, respectively. All of these tested compounds were exhibited higher PTP1B inhibition activities than that of the Na 3 VO 4, a known PTP1B inhibitor used as positive control in present study. Structure activity relationship (SAR) analysis indicated that the inhibition activity of PTP1B was associated with the presence and number of –OH groups.