Medium density polyethylene pipes have been used in the water and gas industries for over a decade. One of the major problems with these pipes is creep under their service pressures. Life prediction is usually based on the secondary creep path until the onset of tertiary creep. Constitutive models such as visco-hyperelasticity and elasto-viscoplasticity can be used to make such prediction. Owing to complexity, the latter is usually used in numerical modeling. Medium density polyethylene is an extremely ductile material with a low modulus of elasticity. The corresponding elongation prior to rupture under a tensile creep test can reach a few hundred percent. The appropriate creep law must be established before any life prediction can be made. In this paper, based on a creep law obtained from a series of material creep tests under different stress levels, a visco-hyperelastic model was developed to simulate Medium density polyethylene pipes under internal creep pressures. Reasonably good correlation has been obtained between the experimental results and the theoretical analysis.