Abstract: The glass forming region of a quaternary system, 0. 30 CuI 0. 70(Cu_2OP_2O_5B_2O_3),was studied, the conductivity and the glass transition temperature of this system weremeasured. In the light of glass structure and chemical bonds, the variations of conductivitywith composition and transition temperature with B_2O_3 content were interpreted. Experimental results show that the quaternary system has better conductivity andthermal stability than that of the original ternary system, CuI-Cu_2O-P_2O_5, from whichthe quaternary system was derived with the introduction of B_2O_3.