Liquid-phase-exfoliation technology was utilized to prepare layered MoS₂, WS₂, and MoSe₂ nanosheets in cyclohexylpyrrolidone. The nonlinear optical response of these nanosheets in dispersions was investigated by observing spatial self-phase modulation (SSPM) using a 488 nm continuous wave laser beam. The diffraction ring patterns of SSPM were found to be distorted along the vertical direction right after the laser traversing the nanosheet dispersions. The nonlinear refractive index of the three transition metal dichalcogenides dispersions n² was measured to be ～10 ⁷ cm²·W ¹, and the third-order nonlinear susceptibility χ⁽³⁾ ～ 10 ⁹ esu. The relative change of effective nonlinear refractive index Δn_2e∕n_2e of the MoS₂, WS₂, and MoSe₂ dispersions can be modulated 0.012– 0.240, 0.029–0.154, and 0.091–0.304, respectively, by changing the incident intensities. Our experimental results imply novel potential application of two-dimensional transition metal dichalcogenides in nonlinear phase modulation devices.