Two new rare 30-norisodinosterol derivatives, 23,24-dimethylcholest-16-ene-3β,5α,6β,11α,20(R)-pentol 3-monoacetate (1) and 23,24-dimethylcholest-16-ene-3β,5α,6β,20(R)-tertrol 3-monoacetate (2), along with a known steroid, 3β,5α,6β,11α,20β-pentahydroxygorgosterol (3), were identified from Xenia umbellata. The structures of the isolated compounds were determined by analyses of the measured spectra (1D and 2D nuclear magnetic resonance, mass spectrometry, and infrared). The biosynthetic pathway of the new norisodinosterols was proposed. Compound 1 exhibited potent cytotoxicity against HepG2, PC-3, and HT-29 with IC₅₀ values of 4.70 ± 0.2, 5.60 ± 0.6, and 4.00 ± 0.4 μg/mL, respectively. On the contrary, compound 3 showed less potent cytotoxicity against HepG2 with IC₅₀ value of 22.20 ± 1.0 μg/mL. Two DNA-binding dyes have been used for the morphological detection of viable, apoptotic, and necrotic cells. The early apoptotic cell death was observed in all types of treated tumour cells. The late apoptotic cells are highly present in HepG2 cells with compound 3 compared with other cancer cells except for compound 1. The anti-proliferative activity of compounds 1 and 3 warranted further investigation.