In this work attempt is made to study the crystallization, microstructure, and magnetic properties of a glass composition of 35% BaO, 35% Fe 2 O 3 , 20% B 2 O 3 , 10% SiO 2 (mol%) without and with 1 mol% extra ZrO 2 as nucleating agent, using various techniques. The formation of BaFe 12 O 19 and BaB 2 O 4 phases as the only crystalline phases formed in a glassy amorphous matrix were confirmed for all of the heat treated samples at their respective DTA exo-peak temperatures. Based on TEM, XRD and DTA results obtained, it was shown that the addition of ZrO 2 promoted bulk crystallization in this system and also acted as a heterogeneous nucleation site for BaFe 12 O 19 phase. Although, the magnitudes of the saturation magnetization (M S ) of all of the heat treated samples were nearly in the same range (25-27 e.m.u./g), the values of the intrinsic coercive field ( i H C ) showed a mch wider range. The addition of ZrO 2 to the glass system studied, have generally gave rise to the decrease of the iH C values. This is thought to be related to the substitution of non-magnetic Zr 4+ ions for Fe 3+ in the barium hexaferrite lattice, weakening the superexhange interaction between Fe sites. The highest values of the i H C of the heat-treated base glass and ZrO 2 added samples were 304 kA/m and 280kA/m, respectively.