Single crystal of pottassium penta borate tetra hydrate an organic material: have been grown byslow evaporation technique at room temperature .The crystalline nature of grown crystal wasconfirmed by power x ray diffraction analysis (XRD). The structure of LKS consists of Li+ andlying on threefold axes and K+ ion has a tetrahedral coordination with Li-O distances 1.909 -1.923 Ǻ. The UV- Vis study was performed to know optical behaviour of the grown crystals.