Dialdehyde 5-aminophenanthroline starch (DASAPL) was synthesized by reacting 5-aminophenanthroline with dialdehyde starch, and it was characterized through elemental analysis, FT-IR, and SEM techniques. FT-IR of DASAPL revealed the incorporation of C=N group and the disappearance of the C=O (carbonyl) group. DASAPL was used to adsorb Cd (II) from aqueous solution. The adsorption process was optimized with regard to pH, contact time, initial Cd (II) concentration, and temperature. The results revealed that the initial pH 5 and contact time of 2 h were the optimal conditions. The material showed good adsorption capacity and the adsorption data followed the Freundlich and Langmuir model. The adsorption of Cd (II) decreased with increasing temperature indicating exothermic nature of the adsorption process. Thermodynamic studies have been used to determine thermodynamic parameters of the process including Gibbs free energy, enthalpy, and entropy changes. Moreover, the adsorbents can be reused.