A new yttrium borate compound K 3 Y 3 (BO 3 ) 4 has been obtained in the K 2 O–Y 2 O 3 –B 2 O 3 ternary system. Its structure, determined from single crystal X-ray diffraction data, shows that it belongs to space group P2 1 /c with unit cell dimensions of a=10.4667(16)Å, b=17.361(3)Å, c=13.781(2)Å and β=110.548(8)°. The structure consists sheets of [Y 8 B 8 O 24 ] ∞ linked by out of sheet BO 3 groups and Y ions to form a three-dimensional framework. The luminescent properties of Eu 3+ and Tb 3+ doped K 3 Y 3 (BO 3 ) 4 materials have also been studied.