Abstract: Objective To study whether the activation of Toll like receptor 1/2 (TLR1/2) has influence on the immune status of umbilical cord mesenchymal stem cell (UCMSC). Methods TLR1/2 agonist Pam3CSK4 was conducted in UCMSC-peripheral blood mononuclear cell (PBMC) co-culture system. Flow cytometry and lactate dehydrogenase (LDH) detection were used to measure the proliferation of PBMC and immune attack of PBMC to UCMSC, respectively. The detection of expressions of co-stimulator and stem cell markers of UCMSC upon TLR1/2 activation was completed by flow cytometry. Real-time PCR was introduced to assay the expression of many immune-related molecules in UCMSC. Cell differentiation staining was conducted to study the change of differentiation ability of UCMSC. Results Activation of TLR1/2 pathway in UCMSC increased the proliferation of PBMC and attack of PBMC to UCMSC, but without influenced the expressions of co-stimulator and stem cell markers. The results of real-time PCR showed that many immune-related molecules were dramatically induced in UCMSC upon TLR1/2 activation, such as 〔interleukin (IL) -2，IL-6，IL-10，IL-12，interferon-γ (IFN-γ), nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α）〕. However, the activation of TLR1/2 had no influence on the differentiation ability of UCMSC. Conclusion Activation of TLR1/2 altered the immune status of UCMSC, including increase the immune attack to UCMSC.