The rubidium molecules Rb-2 and Rb-3 and the cesium molecules Cs-2 and Cs-3 were isolated in argon matrixes and characterized for the first time by Raman spectroscopy. The fundamental frequencies of the dimers were observed at 59.1 cm(-1) for the rubidium dimer and 45.8 cm(-1) for the cesium dimer. The Raman lines of the rubidium trimer appeared at 38.3 and 53.9 cm(-1), and the lines of the cesium trimer, at 24.4 and 39.5 cm(-1). The vibrational frequencies were compared with gas-phase frequencies and with density functional theory (DFT) calculations. Furthermore, the lowest vibrational levels of the (1)Pi(u) state of Cs-2 isolated in solid argon were observed by Raman matrix spectroscopy.