Glasses in the Bi 2 O 3 ?SiO 2 ?ZnO glasses system were examined as a potential replacement for lead-oxide glass frits with low firing temperature ( 500∼600 ? C ) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature( T g ) and thermal expansion coefficient( α ). After forming transparent thick films by a screen-printing method, it was evaluated for the optical properties. The transmittance of thick films fired at 500?600 ? C showed above 80% , which was not dependent on the firing temperature. As a result, many pores were observed at samples fired at low temperature, while the number of pores from samples prepared at high temperature decreased and the pores size increased.