Abstract: The moisture diffusion characteristics of high density polyethylene (HDPE) filled with mica which had been tseated by ethylene plasma of radio frequency were studied through the boiling water immersion experiment.It has been found that the equilibrium moisture.content of filled HDPE increases linearly with the volume fraction of mica,and that the proportional constant is smaller and the data dispersivity naccowed if HDPE was filled with,the treated mica;the larger the mica content is the higher the moisture diffusion verocity,and when the mica content is the same,lower diffusion velocity is found in HDPE filled with plasma treated mica.These are explained by the structure charge of mica/HDPE interface resulted from the plasma treatureat.