The design of cost‐effective biopolymers‐based adsorbents is of particular interest. In our work, a cationic functional starch (CFS)/Na+‐montmorillonite (Na+‐MMT) composite was prepared by combining 5 wt% modified starch containing quaternary ammonium cationic functional groups and 0.5% w/v Na+‐MMT dispersed solution together. Its microstructure was characterized by FTIR and XRD. Removal of three metal anionic ions with different valence like: MnnormalO4−, Cnormalr2normalO72−, and Fe(CN)63− by the composite was compared. Adsorption equilibrium, kinetics, and thermodynamic models were also investigated. The adsorption capacity was very high and followed the sequence of MnnormalO4− > Cnormalr2normalO72− > Fe(CN)63−, which could be demonstrated with strong electrostatic interaction between active cationic functional groups and metal anionic ions. The Langmuir isotherm gave satisfying fits to equilibrium data of MnnormalO4− ions indicating monolayer adsorption to monovalent anionic ion, while the Freundlich equation fitting equilibrium data of Cnormalr2normalO72− and Fe(CN)63− ions better predicated multilayer adsorption to polyvalent anionic ion. There was a better matching accuracy between the experimental data and the pseudo second order model. The removal percentages for the three ions of MnnormalO4−, Cnormalr2normalO72−, Fe(CN)63− by the composite were 96.84, 94, and 89.84%, respectively.