The aim of this study is to produce transgenic mice by testis-mediated gene transfer and investigate the suitable concentration of exogenous DNA for injection. A total of six SPF KM male mice were divided into three groups and liposome-treated exogenous DNA was directly injected into testis at three different concentrations:0. 08 μg /μl,0. 12 μg /μl and 0. 24 μg /μl,respectively. Every treated mouse was naturally mated with 3 female mice on the 5th day after the injection. The spermatozoa were detected on the 20th day after injection under the fluorescence microscope,and mouse testicular paraffin sections were prepared for detection of green fluorescent protein (GFP) expression under fluorescence microscope. The integration of pEGFP-N₁ in the F1 was determined by PCR. The results showed that the proportion of florescent sperm in 3 groups were 9. 09% , 47. 06% and 27. 78% ,respectively. Expression of GFP in different degrees was also found in three groups of paraffin sections. The PCR positive rates of offspring were 17. 26% ,47. 61% and 22. 11% ,respectively. It is concluded that the transgenic mouse could be produced by direct injection of foreign DNA into mouse testis,and 0. 12 μg /μl was the suitable concentration of exogenous DNA for injection in this study.