Objective To investigate the regularity of gene expression and efficiency of gene transfection after tail vein injections of LacZ. Methods After diluting palsmid DNA in PBS solution according to the mouse weight, DNA was transferred via the tail vein by hydrodynamic injection. X-gal staining was performed to measure the LacZ gene expression in the liver, spleen, lung and kidney, Results The naked LacZ plasmid began to express on day 1 post injection, and reached the highest level at day 3, which was about 5%-6%, but diminished drastically by day 7. However, after encapsulated by liposome, the expression level of the same plasmid elevated to 18%-20%, via tail vein hydrodynamic injections. Conclusion High level gene expression in mouse liver can be achieved after tail vein hydrodynamic injections of liposome-encapsulated plasmid DNA, and this technique has great potential for a wide variety of gene therapy studies.