We have prepared lithium zinc silicate (LZS) glasses of compositions (mol%) 17.83Li(2)O-17.73ZnO-(53.52 -x)SiO2-5.25Na(2)O-1.25P(2)O(5)-4.31B(2)O(3)-x-NiO, where 0.5 a parts per thousand currency sign x a parts per thousand currency sign 2.0, by the melt quench technique. The effect of NiO on the phase formation, thermo-physical properties and sealing behaviour of LZS glass-ceramics was studied using X-Ray diffraction (XRD), thermo-mechanical analysis (TMA) and microhardness (MH) measurements. It is found that NiO incorporation leads to a change in the role of ZnO from network modifier to intermediate oxide. The intermediate network forming Zn2+ ions would find it more difficult to diffuse and initiate the transformation of Li3Zn0.5SiO4 to Li2ZnSiO4. Thus Li3Zn0.5SiO4 is formed instead of Li2ZnSiO4 on addition of 2 mol% NiO. Scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) measurements at the glass-ceramic-to-metal interface reveal a change in the microstructure commensurate with the changing role of ZnO. Addition of NiO favoured interdiffusion of species at the interface leading to better sealing.