The crystal structure of the new microporous framework borosilicate |Cs₄|[B₄Si₂₀O₄₈]-CAS has been studied using X-ray diffraction data on powders prepared by solid state reaction as well as by glass crystallization. It is isostructural with |Cs₄|[Al₄Si₂₀O₄₈]-CAS and belongs to the zeolite framework type CAS. Non-random distribution of the Si and B atoms over the tetrahedral positions has been revealed. The behavior of |Cs₄|[B₄Si₂₀O₄₈]-CAS on heating was studied using high-temperature X-ray diffraction HTXRD, differential thermal analysis (DTA) and annealing series. According to HTXRD data the thermal deformation of |Cs₄|[B₄Si₂₀O₄₈]-CAS has anisotropic character with the maximum expansion along the infinite channels, where the Cs atoms are located. The DTA and heat treatment studies showed that during the solid state reaction the first phase to crystallize at about 800 °C is the boropollucite CsBSi₂O₆, which beyond 900 °C transforms into |Cs₄|[B₄Si₂₀O₄₈]. Around 1100 °C a final decomposition occurs according to the reaction |Cs₄|[B₄Si₂₀O₄₈] → 20SiO₂ + 4CsBO₂↑.