A High-density polyethylene has been used for buried plastic pipe production for over a decade. The structural performance of these pipes mainly depends on the viscoelastic properties of using materials. The aim of this study is to determine the creep behavior of PE100 material under constant tensile and flexural stress within 24 hours. In both tests, large deformation occurs within the first 1000 seconds and then very little or no deformation is observed. Primary and secondary creep stages have also been observed.