This paper deals with the effect of span to effective depth ratio, aspect ratio and tensile reinforcement ratio of flat slab on punching behavior of reinforced concrete slab column connection. The experimental program is carried out based on twelve flat slabs of varying dimensions and tensile reinforcement ratio. The test resulst show: (1) the increase in tensile reinforcement ratio improves considerably punching resistance of the test slab - column connection and this increase is directly proportional to specimen size; (2) the decrease of specimen size leads in the increase of the punching resistance, reducing final strain of concrete and rebars and this reduction becomes clearer as tensile reinforcement ratio increases; (3) the increase of the aspect ratio of the slabs affects to punching resistance of the test slab - column connection, however, this effect is reduced as value of the ratio approaches to 2; (4) the tensile rebars are yielded at the failure of the test specimens; angles of the punching shear surface varies from 25° to 32°.