Message RNA-based vaccines with prominent advantages such as facile production, no requirement for nuclear entry and high safety without the need for integration into host genome have been shown to be potent activators of the cytotoxic immune system. However, wider applications of mRNA-based therapeutics have been hindered because of their intrinsically high vulnerability to expressed nucleases and difficulty while entering antigen-presenting cells (APCs) directly. Here, we investigated the potential of cationic lipid-assisted nanoparticles (CLAN), which form a clinically translatable nucleic acid delivery system working as a carrier of an mRNA vaccine. We found that CLAN encapsulating mRNA encoding antigen could effectively stimulate the maturation of dendritic cells (DCs) and promote the activation and proliferation of antigen-specific T cells both in vitro and in vivo. Intravenous immunization of mice with CLAN containing mRNA encoding ovalbumin (OVA) provoked a strong OVA-specific T-cell response and slowed tumor growth in an aggressive E·G7-OVA lymphoma model. Collectively, CLAN proved to be a promising platform for mRNA vaccine delivery.