We have developed the “Grid PSE (Problem Solving Environment) Builder”, a software toolkit that enables users to easily construct a portal system as an interface to the Grid ASP (Application Service Providers). The Grid PSE Builder consists of several distinct components, including single sign-on, file transfer, and job submission. Using the Grid PSE Builder, we have constructed grid portals for several commercially available software packages including Gaussian, a standard software package for quantum chemistry, and Phoenics, a computational fluid dynamics package.