This paper shows a new superplastic forming and diffusion bonding (SPF/DB) method using the low-cost titanium alloy "KS Ti-9". The fundamental superplastic properties of KS Ti-9, which is a low-cost titanium alloy compared with the conventional Ti-6Al-4V, were obtained at various temperatures. The SPF/DB method, which diminishes the wrinkles of the face sheet of a three sheet corrugated core sandwich panel, was developed. Based on these results, the forming process of the three sheet corrugated core sandwich panel was simulated, and a demonstration panel was formed. As a result, it was found that the simulation agreed well with the actual formed panel.