Removal of Cadmium (Cd) from aqueous solution using biochar was considered a cost effective sorbent. Biochar quality and specification depend on its carbonization processes. In this study, the cassava stem biochars were produced at temperature of 300, 400 and 500 °C with slow pyrolysis technique. The biochar in each carbonization temperature was activated with physico-chemical treatments, pre-activated by 1.63M KOH solution then activated with second pyrolysis as same as first pyrolysis conditions. Adsorption study by using biochar adsorb Cd ion from Cd(NO3)2 solution by batch static method. The results indicated that the removal efficiency of activated biochar produced at pyrolysis temperature 300 °C can be increased from 10.46 to 24.88 mg/g and was selected for adsorption characteristic and biochar properties. Adsorption isotherm of non-activated and activated biochar were fitted both Langmuir and Freundlich isotherm (r2>0.95). The BET surface area of activated biochar was increased from 6.8818 to 9.4964 m2/g, while, pore size and chemical properties could be preserved. In summary, our results suggest that KOH pre-activated and second pyrolysis could increase Cd removal efficiency from aqueous solution.