Highly weathered soils, as Latosols (Brazilian Classification Key), generally, present higher phosphorus maximum adsorption capacity (PMAC). This behavior is related with their iron and aluminum oxides contents. Iron oxides can show different PMAC. This fact can vary with some mineralogical attributes as specific surface, pH, ionic strength, and isomorphic substitution. Furthermore, the effect of isomorphic substitution on crystalline (hematite, goethite and maghemote) and poor crystalline iron oxides (ferrihydrite) probably is different. The aim of this work was to evaluate the discrepancies on phosphorus adsorption caused by isomorphic substitution on ferrihydrites. Therefore, 11 ferrihydrite samples (0, 5 or 10 mol% of Cr, Ni, Zn, Pb e Al) were synthetized in the Chemistry and Mineralogy Laboratory at the State University of Maringá - Brazil (LQMS-UEM). The adsorption was evaluated varying pH (from 2 to 11) and ionic strength (0.015 M and 0.15 M NaCl). Chemical (Constant Capacitance Model-CCM) and empirical (Langmuir and Freundlich) surface complexation models were fitted to the data. The CCM was fitted in the FITEQL4.0 software and the empirical models in the Isotherm software. As expected all the ferrihydrites presented high PMAC. Bellow pH 7.0 the adsorption reached maximum (12,000 mg kg^-1) values and started to reduce. Three species were used to adjust the CCM: FeH₂PO₄, FeHPO₄^- e FePO₄^2-. The species FeH₂PO₄ and FePO₄^2- were enough to converge in the 0.015M ionic strength, whereas the specie FeHPO₄^- reduced the quality of the fitting. The same behavior was found to the higher ionic strength (0.15M NaCl). Although the bidentade species were tested, the monodentade species gave the best fitting. Ionic strength and isomorphic substitution did not affect phosphorus adsorption varying the pH. Differences could slightly be observed on Langmuir parameters (PMAC and K) but the CCM 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 shows a high increase in the phosphorus adsorption with the isomorphic substitution.