Objective To investigate the inhibitory effect and mechanism of β-sitosterol on myelodysplastic syndrome (MUTZ-1) in vitro. Methods Three concentrations of β -sitosterol (0 μmoL/L, 10 μmoL/L, 20 μmoL/L) were treated with mutz-1 for 24 h. Cell proliferation rate was detected by CCK-8 method, cell apoptosis rate and cell cycle were detected by flow cytometry. The protein expression levels of Cyclin D1, TGF-β1, p-Smad2 and p-Smad3 were detected by Western blot.Results Compared with 0 μmoL/L group, β -sitosterol of 10 μmoL/L and 20 μmoL/L could inhibit cell proliferation, promote cell apoptosis, prolong cell G1 phase, block cell entering S phase, and decrease the protein expression levels of Cyclin D1, TGF-β1, p-Smad2 and p-Smad3 (P＜0.05). Conclusion β-sitosterol can inhibit the proliferation of MUTz-1 cells, promote cell apoptosis, and disrupt the cell division cycle, which may inhibit TGF-β/Smad signaling pathway in cells