RNA interference is the process that double-stranded RNA (dsRNA) induces the homology-dependent degradation of cognate mRNA mediated by 21- to 23-nt small interfering RNA (siRNA). Successful application of RNAi in functional genomics and proteomics, cancer gene therapy, and virus protection depends on the efficient delivery of siRNA into mammalian cells. The availability of high virus titer, infection of a broad spectrum of cell types, and independence on active cell division makes adenovirus the vector of choice for siRNA delivery. To this end, we developed a new adenovirus shuttle vector designated as pShuttle-H1 to host H1-RNA promoter and unique BglII and HindIII sites for insertion of oligos for expression of siRNA. In this chapter, we describe an adenovirus system that uses a commercially available adenovirus system and pShuttle-H1 to deliver siRNA-expressing cassette into cells to silence a specific gene in mammalian cells.