The Cs-2 3(3)Sigma(+)(g) state, which was observed previously by two-photon excitation [D. Li, F. Xie, Li Li, S. Magnier, V. B. Sovkov, V. S. Ivanov, Chem. Phys. Lett. 441 (2007) 39], has been observed by infrared-infrared (IR-IR) double resonance spectroscopy. One hundred and seventy IR-IR double resonance lines have been assigned to transitions into the 3(3)Sigma(+)(g) v = 2-12 levels. Hyper. ne structure of this state has been resolved in the excitation spectra. Molecular constants and the potential energy curve of this state are reported in this Letter. (c) 2008 Elsevier B.V. All rights reserved.