A material testing apparatus for measuring the biaxial deformation behavior of a polymer1 tube is developed to quantitatively evaluate a deformation behavior of polymeric materials. The testing apparatus is capable of applying an axial force and internal pressure to a tubular specimen. A non-contact strain measurement system is also developed. The system consists of a multi-purpose CCD laser micrometer and an area camera. The biaxial strain components and the radius of curvature in the axial direction of the bulging tube are measured to perform feedback control of the biaxial stress components at the center of the tube. Polyethylene tubes with an outer diameter of 17 mm and a thickness of 2 mm are used as a test specimen, and are subjected to linear stress paths with stress ratios of σφ: σθ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where and are the axial and circumferential stress components applied to the center of the bulging specimen, respectively. Stress-strain curves are successfully measured at a nearly constant logarithmic strain rate of 2×10-3 s-1. The maximum equivalent strain is achieved up to 0.54 at a specimen for σφ: σθ =1:2.