Heavy metals as lead (Pb) can cause environmental contamination on soils and water. Iron oxides are used as powerful adsorbent in these conditions, specially the poor crystalline ones (ferrihydrite). These iron oxides present different adsorption capacities varying with attributes such as surface area, pH, ionic strength and isomorphic substitution. The aim of this work was to evaluate the effect of ferrihydrite isomorphic substitution in lead adsorption. Therefore 11 ferrihydrite samples (0, 5 or 10 mol% of Cr, Ni, Zn, Pb and Al) were synthetized in the Chemistry and Mineralogic Laboratory at the State University of Maringá – Brazil. The adsorption was evaluated varying the pH (from 2 to 11) and the ionic strength (0.015M and 0.15M NaCl). Chemicals (Constant Capacitance Model-CCM and Triple Layer Model-TLM) and empirical (Langmuir and Freundlich) surface complexation models were fitted to the data. The software FITEQL4.0 was used to fit CCM and TLM; Isotherm software was used for empirical models. As expected all the ferrihydrites presented a high lead maximum adsorption capacity (PbMAC). Above pH 5.0 the adsorption was at the maximum for all the samples (38,000 mg kg^-1). The fitting of CCM showed a better convergence when using just a bidentade specie ((FeO)₂Pb) for both ionic strength (0.015 and 0.015M NaCl). However the best fitting for TLM was obtained by adding one outer sphere complex (FeO^-)₂-Pb²⁺. Ionic strength and isomorphic substitution did not affect lead adsorption varying the pH. CCM and TLM showed very similar fitting to all the minerals. This result showed that ferrihydrite has a different behavior comparing with crystalline iron oxides, as goethite, which usually can show a high increase in the lead adsorption with the isomorphic substitution.