The heat transfer and the pressure drop are experimentally studied on the extended heating surfaces with transverse fins for flow direction placed in the air channel of rectangular cross section. From the results of experiment on the effects of fin whose pitch and height are p and l respectively, channel height and Reynolds number, empirical equations for the heat transfer coefficient and the friction factor are presented. It has been shown that the ratio of fin pitch to fin height p/l is a most important factor for the heat transfer and pressure drop performance. In the case of the value of p/l=1.2∼1.6, the finned surface shows the most effective performance. The flow patterns between fins of the surface are observed and the effect of fin materials is also studied experimentally.