The paper reports on the high photocatalytic activity of [Mo6Br8(N-3)(6)](2-) cluster units for the degradation of rhodamine B under UV, visible or sun light irradiation. Water soluble Na-2[Mo6Br8(N-3)(6)] inorganic compound built up from [Mo6Br8(N-3)(6)](2-) anionic cluster units associated with Na+ counter cations investigated in this work is prepared in high yield by the interaction of Mo6Br12 with sodium azide in methanol. The high photocatalytic performance of the molybdenum cluster is demonstrated under real solar light excitation, suggesting that the photocatalyst could be used in broad daylight hours. Furthermore, the cluster is still highly active after ten successive cycling runs under UV or visible light irradiation without any apparent loss of its efficiency.