The effect of thermal annealing on deformation and fracture behavior of residually stressed polyethylene pipes was investigated. Thermal annealing of she pipes simultaneously caused a change in material density and the relaxation of residual stresses. The residual stress relaxation was more sensitive to annealing temperature than annealing time. Annealing at 120℃ for 1 hour removed the residual stresses effectively. While the large deformation properties such as the spilt ring tensile yield strength and the pipe burst strength were affected primarily by the change of crystallinity, the fracture related properties were predominantly affected by the residual stress relaxation. Sustained long term strength and slow crack growth were such properties. It was demonstrated that both of these properties were sensitive to residual stress change and that 100% increase in fracture times was observed as a result of tensile residual stress relaxation. Although the environmental stress cracking resistance (ESCR) test was also conducted to measure the relative clacking behavior the test was not suitable for determining the residual stress effect, as large deformation applied on rung sample effectively removed title residual stresses.