The effect of added MgO nanoparticles on nonlinear optical properties of 6CHBT liquid crystal doped with Sudan black B dye were studied by z-scan technique using of cw He-Ne laser at 632.8 nm. The cell used had homogeneous alignment. The MgO nanoparticles were added to 6CHBT liquid crystal doped with 0.3 wt% Sudan black B dye, at three concentrations of 0.1, 0.3 and 0.6 wt%. It was found that the added MgO nanoparticles did not significantly change the nonlinear refractive index of the compound at concentrations of 0.1 and 0.6 wt% while increasing it at 0.3 wt%.