Abstract: The present study was focused on four kinds of high-frequency electrical resistance welded (HF ERW) pipes with straight seam. By investigating the microstructure and behaviour of welded joint, it is shown that oxide inclusion in joint interfaces is the main factor causing toughness deterioration in electrical resistance welding, especially the low temperature toughness. Moreover, the selection of clean base materials and proper welding technology and welding parameters can substantially decrease the inclusion in joint interfaces so as to obtain HF ERW pipes with high toughness.