Asy (apoptosis/saibousi Yutsudo) is a novel apoptosis-inducing gene found in 1999 by Yutsudo group in Japan. In 2000, Qi Bing et al. cloned another novel gene, named hap (homologue of ASY protein), which encoded the ASY interacting protein, from human lung cell line (WI-38) cDNA library by using yeast two-hybrid system. It has been proved that ASY formed homodimer in yeast and human cell line, ASY and HAP formed heterodimer in yeast cells, and both induced cell apoptosis in human tumor cell lines Sao2 and CGL4. This paper showed that HAP could form homodimer in yeast cells by yeast two-hybrid system; HAP and ASY could produce heterodimer in human cell line by cross-immunoprecipitation test; by using apoptosis-testing technologies such as AnnexinV, TUNEL, DNA ladder and Flow Cytometry, the cell apoptosis in human normal or tumor cell lines transfected with hap or asy individually or cotransfected by the both was qualified or quantified. It was firstly demonstrated that ASY or HAP induced cell apoptosis not only in human tumor cell lines, but also in human normal cell lines. Moreover, we proved that the heterodimer between ASY and HAP decreased apoptosis-inducing activity from the homodimer of ASY or HAP. It revealed that by choosing to form heterodimer or homodimer between ASY and/or HAP is an important mechanism of regulating apoptosis in human cell lines.