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[Display omitted] • Twelve undescribed phytosterols were isolated from Vernonia amygdalina. • The tautomeric equilibrium of isolated phytosterols were investigated. • The anti-cervical cancer activity of isolated compounds was evaluated. • Compound 10 induced HeLa cells apoptosis by activating caspase signaling pathway. • Compound 10 inhibited the HeLa cells proliferation by suppressing the activation of the PI3K/AKT/mTOR pathway. Vernonia amygdalina Delile is generally used as green vegetables for cuisine in Nigeria and health tea or products in southeast of china. It was also used as folk medicine for the treatment of anti-helminth, febrifuge, digestive tonic and wounds. In this study, eleven undescribed phytosterols (1 – 2 , 4 – 12) and six known analogues (3 , 13 – 17) were isolated from the stems of V. amygdalina. Their structures including absolute configurations were elucidated by comprehensive spectroscopic methods (1D and 2D NMR, HRESIMS), X-ray diffraction and comparison of their ECD spectra. Besides, the tautomerism of phytosterols (1 , 3 – 6 , 12 – 17) with hemiacetal moiety were analyzed by solution NMR with different deuterated solvent and variable-temperature experiments. In addition, the cytotoxic activities of isolates against HeLa cells were evaluated. As a result, compound 10 exhibited the most potent anti-cervical cancer activity with the IC 50 of 22.44 μM. Mechanism studies indicated that 10 triggered HeLa cells apoptosis through activating caspase signaling pathway. Furthermore, 10 could arrest the cell cycle in S phase and suppress the activation of the PI3K/AKT/mTOR pathway, leading to the inhibition of HeLa cells proliferation. [ABSTRACT FROM AUTHOR]