The water absorption of high density polyethylene filled with micro hybrid (titanium dioxide and alumina), alumina and titanium dioxide with weight ratio of 15%, 20%, 25% and 30% , are measured in order to study the effect of these particles on water absorption of this polymer. The result shows that the increase of content of filler particles increasing water absorption, because of filler particles which have a higher water absorption percentage than the matrix material, and the filler will take up the free volume within the polymer matrix and create a tortuous path for the water permeating through the sample.