Jack arch slab is still widely used southern Iraq although it is old roof system due to number of practical and economical advantages including simple construction technique, speed in construction, low cost availability of local labor skills. The study of seismic performance of this roofs in south of Iraq is important due to the last earthquakes activity in Iraq and relatively high earthquakes magnitudes of about 6 degrees according to Richter scale, especially in Misan Province. Static tests were conducted to determine the properties of clay brick and gypsum mortar used for jack arch slab in south of Iraq, then the properties of masonry unit is obtained. The effect of camber configuration on ultimate strength and maximum deflection for both flat and 2 cm camber masonry arch specimens is investigated experimentally. The horizontal seismic loads is determined according to UBC while detailed procedure to determine vertical seismic load according to both UBC and Iranian codes is presented due to its govern the design. Finite element numerical analyses are then conducted using STAADPRO software to investigate the effects of a seismic loads on the behavior of slab and evaluate the safety of this type of roofs when subjected to seismic load. It is concluded that the flexural stresses are govern the behavior of jack arch slab not membrane stresses. Based on finite element analysis, the compressive stresses developed in the slab are less than allowable stress but tensile stresses is critical, also the deflection and stresses of IPE steel beams is not exceed the allowable limits