Sawmill wood waste products were used for the biosorption of nickel ions (Ni(II)) from aqueous solution in batch experiments. Effects of physical parameters such as contact time, initial metal concentration, biosorbent dosage, temperature, and pH on the biosorption capacities of both acid-activated sawmill wood waste products (ASWWP) and unactivated sawmill wood waste products (USWWP) were investigated. FT-IR analysis confirmed that hydroxyl, carbonyl, and ether groups are primary contributors to Ni adsorption, through coordination bonding and electrostatic interaction mechanisms. The surface morphology via the SEM images showed a rough, irregular surface structure with porous networks prior to adsorption, but some of the pores were blocked after adsorption. Maximum adsorption capacities of 62.3 and 76.3 mg/g were achieved at 120 and 100 min for USWWP and ASWWP at a pH of 5.0 and initial Ni concentration of 180 mg/L, respectively. The pseudo-first-order kinetic model fit well for the USWWP, whereas the pseudo-second-order kinetic model was well-suited for describing the adsorption of Ni(II) ions on  ASWWP. The values of enthalpy changes (ΔH) for USWWP and ASWWP were 10.2 and 23.4 kJ/mol, respectively, which indicated an endothermic process.