Objective The microglias is the representative of immune cells in the brain. It plays dual roles of both repairing and damaging in injured nervous system, and works as an inevitable component of the circumstance of injured neurons. This study was aiming at the effects of the microglias on the biological activities of mesenchymal stem cells (MSCs) inthe circumstance of injured neurons. Methods MSCs were obtained by primary culture. We adopted PC12 cells (PC12) and BV2 cells (BV2) to substitute for neurons and microglias, respectively. PC12 were injured by aged Aβ1-40 and the supernatant of the injured PC12 was used to set up the circumstance of injured neurons. Transwells were used for co-culture of BV2 and MSCs, which allowed the independent detection of cells after co-culture. Immunofluorescence was used to identify MSCs and neuron-differentiating cells with CD44 and neuron specific enolase (NSE) staining, respectively. MTT assay was adopted to measure the proliferation. Results In the circumstance of both BV2 presence and injured PC12 supernatant incubation, either the proliferation or the differentiation of MSCs reached the highest, which seemed to be contradictory, but we gave our explanations. With the BV2 co-culture, the proliferation of MSCs tend to be higher, but the neuron-differentiating MSCs were similar to those incubated without BV2 co-culture either in normal or injured in PC12 supernatant. With the incubation of injured PC12 supernatant, the neuron-differentiating cells were significantly higher than that of control (P ＜ 0.05). Conclusion In the circumstance of injured neurons, microlgias tend to promote the MSCs proliferation. Although not helpful in neuron-differentiating, microglias did not exert any negative effect either.