Abstract: Objective To explore the influence of protein phosphatase 1A, magnesium dependent, alpha isoform (PPM1A) gene modified human amniotic mesenchymal stem cell (MSCs) on the proliferation in vitro of bladder cancer cell lines T24 and 5637 and the TGFβ/SMAD signaling pathway. Methods Bladder tumor cell lines T24 cells and 5637 cells were cultured in 96-well plates, and four groups were set up, including the control group, MSCs intervention group and PPM1A gene modified group. The cells of the control group were cultured as normal, the cells of MSCs intervention group were co-cultured with MSCs, and the cells of PPM1A gene modified group were co-cultured with MSCs infected by PPM1A over expression lentiviral vector. After 48 h co-culture, PPM1A mRNA expression was detected by RT-PCR assay, the protein expression of TGF-β pathway associated markers such as TGF-β, TGF-βⅡ receptor (TβRⅡ), p-Samd2/Samd2 and p-Samd3/Samd3 were detected by WB assay. Results Compared with the control group, the growth rate of T24 and 5637 cells of MSCs intervention group was reduced, the TGF-β, TβRⅡ, p-Samd2/Samd2 and p-Samd3/Samd3 expression levels were decreased, and compared with MSCs intervention group, the growth rate of T24 and 5637 cells of PPM1A gene modified group was reduced, the TGF-β, TβRⅡ, p-Samd2/Samd2 and p-Samd3/Samd3 expression levels were decreased, and the difference between groups was statistically significant (P<0.05). Conclusion MSCs modified by PPM1A can inhibit the expression of TGF-β pathway, thus limiting the malignant proliferation of T24 and 5637 in bladder tumor cell lines, which may be one of its important mechanisms to anti-tumor.