The structural behavior of the non-linear optical, nanoporous compound CsLiB6O10 was studied in a wide temperature range. Both the highly anisotropic thermal expansion of the borate with temperature variation and the deterioration of its crystals were investigated. The electron density distribution was analyzed in detail. A reversible, partial transition to a new modification, beta-CsLiB6O10, was observed during cooling crystalline and moist samples of CsLiB6O10 to -25 degrees C. The crystal structure of the new phase is described.