Biaxial loading experiments for a seamless steel tube subjected to prestraining are carried out using a servo-controlled multiaxial tube expansion testing machine. This testing apparatus is capable of applying arbitrary biaxial stress paths to the central section of a tubular specimen by controlling axial forces and internal hydraulic pressure. The tubular specimens are loaded via linear and bilinear stress paths. Contours of plastic work of the as-received material are measured by linear stress path experiments. Bilinear stress path experiments are performed to investigate the effect of axial compressive prestraining on the stress-strain curves in the subsequent biaxial loading. In addition, small uniaxial tensile specimens are machined from the axial and hoop directions of the mother tube wall, and tension-compression reverse loading experiments are performed to quantitatively evaluate the Bauschinger effect of the test material. It is experimentally found that the Bauschinger effect observed in uniaxial reverse loading and biaxial reloading can be reproduced by kinematic hardening models and that the associated flow rule is almost satisfied with the yield locus used in the kinematic hardening models. The material model will be useful in improving the accuracy of numerical analyses of the cold-working processes for fabricating steel tubes.