A plasma surface treatment of HDPE has been carried out in a fluidized bed. The effects of operation parameters on the surface composition and hydrophilicity have been determined. The oxygen functionalities are formed at the outermost layer of HDPE powder. The hydrophobic surface of HDPE powder has been transformed to hydrophilic surface by the oxygen-plasma treatment in a fluidized bed. The contact angle of the plasma treated HDPE powder decreases linearly with radio frequency (rf) power but increases with O2 flow rate. Also, the angle decreases with increasing the composite parameter as the total plasma energy down to 6,000 [(W/FM)t]. The contact angle has been correlated with the composite parameter as : theta = 90-6.64x10(-3) [(W/FM)t].