The parallel plate load test is used to measure "pipe stiffness" for HDPE pipe. Pipe stiffness is employed as a measure of pipe resistance to bending deformation as well as a quality control index for the manufacturing process. This work presents the results of a series of parallel plate tests conducted on profiled HDPE plastic pipes to determine ring stiffness values. During the study, all pipe samples were tested according to the DIN 16961 2:2010-03 standard. The nominal inside diameters of the test pipes were selected 500 and 600mm. These pipes compressed radially a constant load during 24 hours and deflection were measured by a comparator. Then experimental ring stiffness values were calculated by using these data.