Nanocrystalline lithium-substituted manganese-zinc ferrites Li0.5xMn0.4Zn0.6-xFe2+0.5xO4 were prepared by the sol-gel autocombustion method. X-ray diffraction analysis (XRD) confirmed that samples are single-phase and that only a spinel phase is present. The saturation magnetization increases while the cell parameter of the cubic phase decreases with Li concentration. Magnetic permeability and dielectric permittivity of all samples were measured at room temperature as a function of frequency. Reflection loss calculations show that the prepared samples are good electromagnetic wave absorbers in microwave range. Li substitution plays an important role in changing the structural and magnetic properties of these MnZn ferrites.