Majority of buildings in Turkey and in most developing countries are made with reinforced concrete frames infilled with clay tile brick walls. Despite this, influence of these walls is not accounted for in design. Past earthquake observations have shown that the infill walls have great influence on performance of buildings. In this paper, influence of the brick infill walls on strength and stiffness of RC buildings are presented through analytical results obtained for some typical buildings. Comparison of results showed that stiffness of the walls and their capacity is greatly influenced by the infill walls. The change in the strength and stiffness has been based on ratio of the wall area to the total floor area with providing expressions to determine these.