Therapeutics based on small interfering RNA (siRNA) have a great clinical potential; however, delivery problems have limited their clinical efficacy, and new siRNA delivery vehicles are greatly needed. In this report, we demonstrate that submicron particles (800-900 nm) composed of the polyketal PK3 and chloroquine, termed as the PKCNs, can deliver tumor necrosis factor-alpha (TNF-alpha) siRNA in vivo to Kupffer cells efficiently and inhibit gene expression in the liver at concentrations as low as 3.5 microg/kg. The high delivery efficiency of the PKCNs arises from the unique properties of PK3, which can protect siRNA from serum nucleases, stimulate cell uptake and trigger a colloid osmotic disruption of the phagosome and release encapsulated siRNA into the cell cytoplasm. We anticipate numerous applications of the PKCNs for siRNA delivery to macrophages, given their high delivery efficiency, and the central role of macrophages in causing diseases such as hepatitis, liver cirrhosis and chronic renal disease.