Mechanical and electrical responses of graphite powder (GP)-filled high-density polyethylene composites to a uniaxial compression-decompression cycle were studied. Above a compression loading level, a large positive-pressure coefficient effect of resistance was observed, for which a slide mechanism of GP in the matrix is believed to be responsible. In a step-wise compressive loading and loading-holding experiment, the critical compression level was also found, at which the resistance response changed from a time-independent one to a time-dependent, creep-like one. The current-voltage behavior of the composites showed that the GP contact was non-ohmic, regardless of GP contents and pressure levels.