Polyaniline/attapulgite (PANI/ATP) nanocomposites doped by hydrochloric acid (HCl) were prepared by in-situ polymerization method. The structure and absorption mechanism for eriochrome blue black of nanocomposite were investigated. Amount of absorbent and influence of pH for absorbent effect were also studied. The results reveal that the nanocomposites have not only the structure of ATP but also the property of the PANI. The nanocomposites hold an excellent adsorption for eriochrome blue black when the pH value is 5. The adsorption thermodynamics of the nanocomposites follows the Langmuir isothermal adsorption equation. The maximum adsorption capacity can reach 192.67mg/g. The calculate results show that the adsorption enthalpy is 4.15kJ/mol, the Gibbs free energy is (–22.98 to –19.26) kJ/mol, and the entropy of 81J/(mol·K), which imply that the adsorption is an endothermal and spontaneous process.