Abstract: The two-dimensional Ti₃C₂T_x was modified by sulfonic acid group grafting (abbreviated as Ti₃C₂T_x—SO₃H), and its microstructure before and after the modification was characterized. The adsorption behavior and mechanism of heavy metal Pb²⁺ by the Ti₃C₂T_x—SO₃H were also investigated. XRD, FTIR and EDS analyses indicate that sulfonic acid group is successfully grafted on the surface of the Ti₃C₂T_x, while SEM shows that the Ti₃C₂T_x—SO₃H has a lighter and thinner layered structure than the Ti₃C₂T_x. Pb²⁺ adsorption by the Ti₃C₂T_x—SO₃H reaches equilibrium within 20 minutes. The maximum adsorption capacity of the Ti₃C₂T_x—SO₃H is 733.6 mg·g⁻¹, which is 23% higher than the Ti₃C₂T_x. And Pb²⁺ adsorption capacity by the Ti₃C₂T_x—SO₃H gradually increases with the increase of pH (2-6). Under the interference of coexisting ions such as Mg²⁺, Ca²⁺, Co²⁺ and Zn²⁺, the Ti₃C₂T_x-SO₃H still maintains a high level of Pb²⁺ adsorption. Pb²⁺ adsorption processes by both the Ti₃C₂T_x and the Ti₃C₂T_x—SO₃H fit well the pseudo second kinetic model and Langmuir isotherm model, suggesting that the adsorption processes are monolayer chemisorption. The Ti₃C₂T_x—SO₃H shows more excellent adsorption performance towards Pb²⁺ after adsorption mainly due to the more active sites provided by sulfonic acid group and the enhanced dispersion in aqueous solution.