In this study, highly porous polyetheretherketone (PEEK) foams were produced by space holder-powder sintering method for bone substitute material and load-bearing orthopaedic hard tissue (knee, hip or spinal) implant applications. NaCl and carbamide powders were used as a space holder (pore former). PEEK has good chemical resistance, radiolucency, sterilization resistance, and mechanical properties close to bone. However, chemical and biological inertness and hydrophobic surface nature of the PEEK limits the bone attachment. Open pores can provide channels for the bone attachment and body fluid transmission, which is beneficial for implant fixation. In addition, sulfonation surface treatment was carried out in sulfuric acid to enhance the bioactivity. Wettability (contact angle) of the samples was investigated by using optical tensiometer. Wetting behaviour of the samples was increased with sulfonation. Apatite-forming ability (bioactivity) of the sulfonated samples was evaluated in simulated body fluid. Sulfonated foams were exhibited improved bioactivity due to the micro-porous surface structure and hydrophilic SO3H functional groups. Mechanical properties of the foams were also studied.