Objective To evaluate the effect of mesenchymal stem cell (MSC) coated-islets on instant blood-mediated inflammatory reaction (IBMIR) after islet transplantation. Methods MSC labeled with tracer and human islets were placed into an ultra-low adsorption cell culture dish, shaken and mixed twice at an interval of 0.5 h, and then incubated at 37 ℃ and 5% CO2 for 24 h to obtain MSC-coated islets. The coating effect of MSC and in vitro function of the islets were assessed. A blood circulation tube-shaped model was established in vitro. In the blank control group, 0.2 mL of islet culture solution was added. In the islet group, 800 islet equivalent quantity (IEQ) of uncoated islets were supplemented. In the MSC-coated islets group, 800 IEQ of MSC-coated islets were added, and circulated for 60 min at 37 ℃. A portion of 0.5 mL blood sample was taken for routine blood test at 0, 30 and 60 min, respectively. After 60 min circulation, the blood sample was filtered with a 70 μm filter to collect plasma, blood clots and islets. Blood clots and islets were subject to hematoxylin-eosin (HE) staining and immunohistochemical staining. Morphological changes and the aggregation of CD11b-positive cells surrounding the islets were observed. The contents of plasma thrombin-antithrombin complex (TAT), tissue factor (TF), C3a, C5b-9, interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1 and IL-8 were determined by enzyme-linked immune absorbent assay. Results After 24 h co-incubation, the islets were coated by MSC, with a coating degree of approximately 80%. In the islet and MSC-coated islet group, a large quantity of neutrophils and monocytes were observed surrounding the blood clots and islets, and the quantity of CD11b-positive cells in the MSC-coated islet group was less compared with that in the islet group. After co-incubation with the whole blood for 0, 30 and 60 min, the quantity of platelets, neutrophils and monocytes was declined in the MSC-coated and islet groups, and gradually decreased over time. Compared with the blank control group, the quantity of platelets, monocytes and neutrophils was lower, whereas the TF content was higher in the MSC-coated islet group. Compared with the islet group, the quantity of platelets, monocytes and neutrophils was higher, whereas the TAT and TF contents were less in the MSC-coated islet group, the differences were statistically significant (all P < 0.05). Compared with the blank control group, the expression levels of C3a, C5b-9, IL-6, TNF-α and IL-8 were up-regulated in the MSC-coated islet group. Compared with the islet group, the expression levels of C3a, C5b-9, IL-1β, IL-6, TNF-α, IL-8 and MCP-1 were down-regulated in the MSC-coated islet group, and the differences were statistically significant (all P < 0.05). Conclusions MSC-coated islets may reduce the exposure of islet TF in the blood and prevent the incidence of IBMIR during the coagulation response stage, thereby mitigating the injury and loss of islet allograft in the early stage of islet transplantation.