Measurements of magnetic susceptibility have been made on the Li_xMn_<l-x>Se system at temperatures ranging from 77 K to room temperature. The curves of the susceptibility obtained show a thermal hysteresis. The values of the effective magnetic moments per Mn atom decrease with increasing Li concentration. . However, these values are lower than those expected on the consideration of Li^+_xMn^+++_xMn^++_<1-2x>Se. The values of the paramagnetic Curie temperature increase with increasing Li concentration.