Transgenic mice were produced by introduced exogene construct lambda 106, an expression construct of HBsAg gene directed by bovine alpha-S1 casein gene, with microinjection. Gene integration test with PCR-Southern hybridization, shows that the construct integration rate is 56% (17/30) and expressed rate, by ELISA, of target gene product HBsAg is 100% (8/8) in the first generation. Generation trailing test suggests that the gene construct can be stably inherited across generation after generation, and expressed more or less than parents among offspring. However positive rate of offspring does not follow genetic ratio that exogenous gene can be integrated randomly into a single site on chromosomes. There may be a machinery of multi-sites for exo-gene integration. Changes of the target gene expression in the offsprings may be related to position effect, changing of gene copy number and changing of chromatin imprinting pattern when parent's genome information was delivered to their progeny.