Abstract: This study aims to generate the mechanical responseof plain high-strength high-performance concrete (HSHPC) subjectedto biaxial compressive loading at seven stress ratios, \alpha =\sigma _2 : \sigma_ 3,-0.00: -1, -0.20: -1, -0.30: -1, -0.40: -1, -0.50: -1, -0.75: -1,-1.00: -1, after exposure to the temperature of 20^\circC,200^\circC, 300^\circC, 400^\circC, 500^\circC and600^\circC, using thetrue-triaxial loading system. The biaxial static compressivestrengths, strains at the peak stress and the stress-strain curves areobtained to analyze the influence of the temperature and the stress ratio.Failure modes of plain HSHPC specimens are observed. The experimentalresults show that the biaxial compressive strength of HSHPC is moresensitive to the stress ratio and the exposure treatment to hightemperatures than the uniaxial compressive strength. The Kupfer-Gerstlefailure criterion for plain HSHPC is developed with the parameters of thetemperature and stress ratio.