Due to the excellent mechanical and spectrum properties, Co∶MgAl2O4 is an important saturable absorber (SA), which can be applied as a medium for the passive Q-switching operation of solid lasers with the wavelength of 1.5 μm-the "eye safe" lasers.In this work, Co∶MgAl2O4 nanopowders were synthesized via the co-precipitation method using the mixed solution of ammonia and ammonium carbonate as the precipitant.The effects of different metal-ions and precipitant concentrations on the chemical compositions and microstructures of the particles were investigated.The X-ray diffraction analysis showed that all the powders calcined at above 1000℃ were single spinel phase.Especially, when the molar ratio of metal-ions, ammonium carbonate and ammonia was 3∶4∶3, the mono-disperse spinel powders were prepared by calcining the precursor at 1100℃ for 4 h in air, and the chemical composition of powders was approximate to the stoichiometric magnesium aluminate spinel.Using the calcined spinel powders without sintering additives as raw materials, Co∶MgAl2O4 transparent ceramics were produced by vacuum sintering at 1600℃ for 2 h, followed by the post-treatment of HIP for 3 h at 1600℃ in Ar atmosphere of 200 MPa.In the transmittance curves of Co∶MgAl2O4 ceramics, there was a strong absorption in wavelength range of 1.2~1.6μm, which was probable to realize the Q-switching operation.