A cross-linked chitosan (denoted as TCCS) was synthesized by dissolving chitosan in acidic aqueous solution and addition of minimum amount of terephthaldehyde as cross-linker, the synthesized polymer was characterized by Fourier-transform infrared spectroscopy (FT IR) and scanning electron microscopy (SEM). TCCS was used as an adsorbent to remove the organic dye congo red (CR) from aqueous solutions. The effects of contact time, pH, adsorbent weight, and initial dye concentration were studied. The results indicated the 0.02 g of TCCS can remove more than 98% of CR form 25 ml aqueous solution with 40 ppm solution after 60 min with no significant effect observed with changing the pH. Langmuir, Freundlich, and Temkin isotherm models were implemented to on the experimental data, the best fit was with Langmuir isotherm model, the correlation coefficient (R2) value for this isotherm was (0.998), while for Freundlich, and Temkin isotherms the R2 values were 0.8824 and 0.933 respectively. The results of the kinetic studies revealed that the adsorption of CR on TCCS is a pseudo second order process, with R2 value of 0.9982, and the calculated adsorption capacity (qe) values for this model 49.26 mg/g, which is very close to the experimental result (49.04 mg/g). The thermodynamic parameters indicated that the adsorption of CR on TCCS is spontaneous with negative ΔG values, endothermic with positive ΔH and positive ΔS which indicates that the disorder of the CR molecules increases at the adsorbent-solution interface.