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In the investigation of MgO-Y2O3-B2O3 system,six three-phase regions,five binary compounds and one ternary compound MgYB5O10 are confirmed in the subsolidus phase relations.Single-phase powder sample of MgYB5O10 is successfully prepared through solution synthesis method which can effectively restrain the generation of the second-phase impurities.Determined from the step-scanning X-ray powder diffraction data by using the Rietveld method,it can be learned that MgYB5O10 crystallizes in the monoclinic system in the space group P121/c1 and lattice parameters a=8.51132(6)(A),b=7.58914(9)(A),c=12.24603(5)(A),β=130.20004(3)°,Z=4,and final agreement factors Rp=2.55%,RWP=3.20%..Composed ofMgO6,YO10,BO3 and BO4 basic groups,the 3-dimensional framework of MgYB5O10 can be considered as a set of parallel 2-dimensional [B5O10]5-n layers composed of three BO4 tetrahedra and two BO3 triangles sharing comers linked together by Mg and Y atoms.The existence of BO3 and BO4 groups has been further verified by infrared spectra.The uv-vis spectrum shows strong absorption within the range of 200 to 400nm,but negligible in the visible area,which can also leads to the determination of band gap 2.72eV.It promotes great possibilities for MgYB5O10 being diverse phosphors by different doping.