To understand the effect of collagen peptides on the function of mouse lymphocytes under simulated microgravity. The splenocytes of mice were isolated, and the rotary cell culture system was used to simulate the microgravity. The T lymphocytes were stimulated with mitotic agents, concanavalin A (ConA), and the cells were treated with different concentrations of collagen peptides. The proliferation of lymphocytes and the levels of cytokines in the supernatant were detected. Simulated microgravity could inhibit the proliferation of spleen T lymphocytes and decrease the level of cytokines in the supernatant. Collagen peptides could promote the lymphocyte proliferation and cytokine production in cells cultured under simulated microgravity. Collagen peptides may attenuate the inhibitory effect of simulated microgravity on T lymphocytes by regulating the cell proliferation and the secretion of cytokines.