Spinel Li CoMnO4 is prepared by solid-state reaction and its magnetic properties are comprehensively studied by direct current(DC) and alternating current(AC) susceptibilities, isothermal remanent magnetizations, and magnetic hysteresis.Fitting to the Curie–Weiss law by using high-temperature zero-field-cooled susceptibility confirms a low-spin state of Co3+with S = 0. Both the fitting parameters first increase and then tend to be saturated at high magnetic fields through using isothermal remanent magnetizations, which suggests a spin glass transition at low temperature. AC susceptibility study also supports this conclusion since the frequency dependence of peak position and intensity follows the tendency of a spin glass transition. The origin of the spin-glass transition in Li CoMnO4 might be attributed to a spatial segregation between non-magnetic Co3+regions and spin glass ordered regions of Mn4+ions. Spinel Li CoMnO4 is prepared by solid-state reaction and its magnetic properties are fully studied by direct current (DC) and alternating current (AC) susceptibilities, isothermal remanent magnetizations, and magnetic hysteresis. Fitting to the Curie-Weiss law by using high- temperature zero-field-cooled susceptibility confirms a low-spin state of Co3 + with S = 0. Both the fitting parameters first increase and then tend to be saturated at high magnetic fields through using isothermal remanent magnetizations, which suggests a spin glass transition at low temperature. AC susceptibility study also supports this conclusion since the frequency dependence of peak position and intensity follows the tendency of a spin glass transition. The origin of the spin-glass transition in Li CoMnO4 might be attributed to a spatial segregation between non-magnetic Co3 + regions and spin glass ordered regions of Mn4 + ions.