This paper investigates the mechanical properties of high strength steel (HSS) RQT 701 at elevated temperatures. The investigated parameters were relative thermal elongation, elastic modulus, effective yield strengths, and stress-strain relations. Tensile tests were carried out at elevated temperature by both steady-state and transient-state methods. The test results were compared with those for unheattreated carbon steels (normal steels) with grades up to S460 as in EN 1993-1-2. The comparisons indicate that RQT 701 steel has smaller relative thermal elongation than normal steels. Its effective yield strength and elastic modulus reduce faster than those of normal steels at high temperatures. The elasic moduli obtained from transient-state tests are smaller than those from steady-state tests and normal steels.