The purpose of this report is to elucidate influence of welding conditions on seam weldability of a surface-finished steel sheet. The analytical equation for temperature rising in welding was obtained by means of Joule＇s heating law for the proposal welding model. Then, the relation between the weldability and the welding condition was considered. The experimental results are as follows. 1 Weldability becomes poor with an increase in welding speed. 2 Weldability improves with increasing current frequency. 3 Weldability improves with an increase in applied force. From the analytical equation, temperature at the end of the current path (exit point of electrode) changes periodically with current frequency and these deviations increase with increasing speed, decreasing current frequency and decreasing current path. It is considered that "Splash" is easy to cause, as much as the wider temperature deviation, and then weldability becomes poor. These analytical results may support the experimental results qualitatively.