The crystal of (24R)-3β,5α-dihydroxy-24-ethyl-5α-cholestan-6-one (1) was isolated from the leaves of P. nagi planted in Fujian for the first time with the same skeleton as 26,27-dinorcholest-5-en-3-β-ol (2) and β-sitosterol (3) that have been reported before. Compound 1 crystallizes in monoclinic, space group P2₁ with a = 10.8482(4), b = 7.3671(3), c = 33.7860(15) Å, β = 93.103(4)°, V = 2696.21(19) ų, Z = 75, M_r = 446.70, ρ_calc = 1.145 g/cm³, F(000) = 1032, μ = 0.572 mm^–1, GOOF = 1.034, the final R = 0.0467 and wR = 0.1129 for 6989 observed reflections with I > 2σ(I). Compound 2 was selected to evaluate for their preliminary in vitro anticancer activity against four cancer cell lines for the first time. The results showed that compound 2 exhibited great inhibition against gastric cancer, breast cancer MCF-7, lung cancer A549 and Helacell lines with the inhibitions of 89.16% ±1.17, 97.02%±0.53, 47.20% ±2.58 and 36.89%±1.22 respectively at the concentration of 1.4×10^-2 M, which means that we found the new anticancer compound in this plant medicine.