To investigate the effect of D-ferrite on the hot workability and surface defect of STS 304 billets containing 3 wt. % Cu, microstructure observations and high temperature mechanical properties test were carried out for the specimens extracted mainly from raw or oxidized billets. It was found that the total $delta$-ferrite content has little influence on the hot workability, even though the fracture cracks due to high temperature tension or compression test were initiated and propagated mostly along $delta$/${gamma}$ boundary in the specimens. On the other hand, it was supposed that the direct causes of surface defects in the wire rolled from the as-continuously cast billet were the grain boundary embrittlement arose from the deep diffusion of oxygen into the grain boundary, and the oxidation of $delta$-ferrite connected by a grain boundary to the surface during the billet reheating process as well.