Aim:The purpose of this study is to evaluate the retention of PEEKbased posterior crowns after different surface treatment protocols(sandblasting using110micron alumina particles,acidetching using sulphuricacid and combined sandblasting and acidetching).Methodology:24extracted human natural molars that were mounted in epoxy blocks and they were prepared to receive PEEK copings that were divided into3groups.The first group was treated withsandblastingwith110micron alumina particles under 2bar,The second group was treated with98%sulphuric acid for60seconds then rinsed with running water for60seconds,The third group was treated with sandblasting and acid etching together then all copings were cemented to their corresponding teeth withRelyxUltimate clicker then after cementation all copings were subjected to a pull out test using aUniversal testing machine.After the mesurments the teeth were examined under digital microscope to detect the mode of failure.Results:For Sandblasted group the mean±SD values were(80.66±5.54N)with minimum value(59.31N) and maximum value(108.27N),while for Acid etched group the mean±SD values were(87.45±5.56N)with minimum value(81.96N)and maximum value(101.34N).Meanwhile the mean±SD values for Sandblasted and Acid etched group together were(92.43±5.51N)with minimum value(79.67N)and maximum value(106.19N).In accordance to the mode of failure In SB and AE treated group,the failure mode pattern was predominantly adhesive while minority was mixed.In SB+AE treated group samples showed equal%between adhesive and mixed failure mode patterns.There was no record for cohesive failure mode pattern in all groups.Conclusions:Within the limitation of this study;The surface treatment that was preformed by using sandblasting and sulphuric acid etching togethere showed the highest results in accordance to retention of the copings.The use of different surface treatment protocols gives a reliable results in accordance to retention.