It is well known that the Alkali-Silica Reaction (ASR) expansion in concrete is influenced by the stress state of the material. However, the extent and nature of this influence is not completely understood due to the scarcity of experimental investigation under triaxial stress states. This paper presents experimental ASR expansion curves obtained from cubical concrete specimens subjected to three different triaxial stress states, by means of a new testing machine especially designed for this purpose. The results seem to confirm that the volumetric ASR expansion rate is reduced as the applied volumetric compressive stress is increased. Additionally, there seems to be an increase of the expansion rate in the less compressed direction in detriment of the expansion rates in the most compressed ones.