Thoroughly understanding the behaviour of concrete in dynamic loading is an issue of great significance in civil engineering. However, our knowledge is limited by a lack of dynamic experiment database, especially that collected by dynamic multiaxial tests. Biaxial compressive experiments on 100 mm concrete cubes were performed using a servo-hydraulic multiaxial testing system designed and manufactured at Dalian University of Technology, China. The specimens were loaded in biaxial stress states. The lateral pressure was maintained at a fixed proportion to the axial load, with the stress ratios of 0:1, 0·25:1, 0·5:1, 0·75:1, 1:1 respectively. The strain rate varied from 10−5/s to 10−2/s. From the test results it is revealed that the dynamic strength increases as the strain rate increases, while the damage pattern and the ultimate strength are closely related to the magnitude of lateral pressure exerted on the specimen. The shapes of stress–strain curves of the specimens at different strain rates are similar to each other. A unified formula is proposed to characterise both the effect of strain rate and the effect of stress ratio on the ultimate strength of concrete in biaxial stress states.