The focus of this work is to develop accurate multiscale failure criterion for superplastic deformation that can be used to optimize SPF. The multiscale failure criterion accounts for both geometrical instabilities (necking) and microstructural features including grain growth and cavitation. The multiscale failure criterion is incorporated in a FE code to simulate and optimize SPF by designing variable strain rate forming paths based on the developed failure criterion. The results show that following this optimization approach, the forming time can be significantly reduced while maintaining the uniformity of the formed part.