Nucleic acid-based therapy has become an increasingly important strategy for treating a variety of human diseases. In systemic therapy, a therapeutic gene must be delivered efficiently to its target tissues without side effects. To deliver a therapeutic gene such as plasmid DNA (pDNA) or small interfering RNA (siRNA) to target tissues by systemic administration, cationic carriers such as cationic liposomes and polymers have been commonly used as a non-viral vector. However, the binary complex of therapeutic gene and cationic carrier must be stabilized in the blood circulation by avoiding agglutination with blood components, because electrostatic interactions between positively charged complexes and negatively charged erythrocytes can cause agglutination, and the agglutinates contribute to high entrapment of the therapeutic genes in the highly extended lung capillaries. One promising approach for overcoming this problem is modification of the surface of cationic complexes with anionic biodegradable polymers such as hyaluronic acid, chondroitin sulfate, or polyglutamic acid. As another approach, we recently developed a sequential injection method of anionic polymer and cationic liposome/therapeutic gene complex (cationic lipoplex) for delivery of a therapeutic gene into the liver or liver metastasis. In this review, we describe recent advances in the delivery of therapeutic genes by lipid- and polymer-based carrier systems using anionic polymers.