Rheumatoid arthritis (RA) is a common autoimmune disease, which is characterized by painful chronic inflammation in the joints, and novel safe and efficacious treatments are urgently needed. RNA interference (RNAi) therapy based on small interfering RNA (siRNA) is a promising approach for silencing specific genes involved in inflammation. However, delivery of siRNA to the target site, i.e. the cytosol of immune cells, is a challenge. Here, we designed lipid-polymer hybrid nanoparticles (LPNs) composed of lipidoid and poly(DL-lactic-co-glycolic acid) loaded with a therapeutic cargo siRNA directed against the proinflammatory cytokine tumor necrosis factor (TNF), which plays a key role in the progression of RA. We compared their efficacy and safety with reference lipidoid-based stable nucleic acid lipid particles (SNALPs) in vitro and in vivo. Cryogenic transmission electron microscopy, atomic force microscopy and small-angle X-ray scattering revealed that the mode of loading of siRNA in lamellar structures differs between the two formulations. Thus, siRNA was tightly packed in LPNs, while LPNs displayed lower adhesion than SNALPs. The LPNs mediated a higher TNF silencing effect in vitro than SNALPs in the RAW 264.7 macrophage cell line activated with lipopolysaccharide. For both types of delivery systems, macropinocytosis was involved in cellular uptake. In addition, clathrin-mediated endocytosis contributed to uptake of SNALPs. LPNs loaded with TNF siRNA mediated sequence-specific suppression of inflammation in a murine experimental arthritis model upon intra-articular administration. Hence, the present study demonstrates that LPN-mediated TNF knockdown constitutes a promising approach for arthritis therapy of TNF-mediated chronic inflammatory conditions.