We report results of X-ray diffraction (XRD) and valence band X-ray photoelectron (VB-XPS) spectra for strontium borate Sr2B16O26. The X-ray structural analysis shows that the single crystals of Sr2B16O26 crystallize in the monoclinic space group P2(1)lc with a = 8.408(1) angstrom, b = 16.672(1) angstrom, c = 13.901(2) angstrom, beta = 106.33( 1)degrees, and Z = 4. The crystal structure consists of a 3D network of the complex borate anion [B16O20O12/2](4-), formed by 12 BO3 triangles and four BO4 tetrahedra, which can be viewed as three linked [B3O3O4/2](-) triborate groups bonded to one pentaborate [B5O6O4/2](-) group and two BO3 triangles. Using this structure, we have performed theoretical calculations using the all-electron full potential linearized augmented plane wave (FP-LAPW) method for the hand Structure, density of states, electron charge density, and the frequency-dependent optical properties. Our experimental VB-XPS of Sr2B16O26 is compared with results of our FP-LAPW calculations. Our calculations show that the valence hand maximum (VBM) and conduction hand minimum (CBM) are located at Gamma of the Brillouin zone (BZ) resulting in a direct energy gap of about 5.31 eV. Our measured VB-XPS show reasonable agreement with Our calculated total density of states for the valence band that is attributed to the use of the full potential method.