We examined whether sonoporation enhanced by a contrast agent (BR14) was effective in gene therapy for hepatocelluar carcinoma (HCC). Human hepatic cancer cells (SK-Hep1) and plasmid cDNAs expressing green fluorescent protein (GFP), interferon beta (IFN beta), and LacZ were used. In vitro, SK-Hep1 cell suspensions with DNA and BR14 were sonoporated. Expressions of every plasmid cDNA and the antitumor effect of IFN beta were analyzed. In vivo, GFP and IFN beta genes with BR14 were directly injected into subcutaneous tumors using SK-Hep1 in nude mice, and transcutaneous sonoporation of the tumors was performed. GFP gene transfections and tumor diameters after IFN beta gene transfection were examined. In vitro, no SK-Hep1 cells were transfected without sonication, whereas transfections were successful after sonication with BR14. Antitumor effect of IFN beta gene transfection by ultrasound (US) and with BR14 was revealed. In vivo, the SK-Hep1 cells expressed GFP, and the IFN beta gene transfection by US with BR14 reduced tumor size significantly. In conclusion, gene therapy with sonoporation enhanced by a contrast agent may become a new treatment option for HCC.