pDOR-p21 sense and pDOR-p21 antisense retroviral expression vectors were constructed and successfully transfected by Lipofectin into normal human diploid fibroblasts(2BS line), resulting in 2BS-p21s and 2BS-p21a cell lines, respectively. Southern blot analysis verified that the exogenous p21(WAF1) cDNA were integrated into genomic DNA. Compared with the cells transfected with pDOR-neo empty vector, p21(WAF1) mRNA expression increased in 2BS-p21s cells, which were less sensitive to apoptosis induced by NaBu, and showed higher cell viability, delayed appearance of DNA ladder, and less area of apoptosis peak. On the other hand, p21(WAF1) mRNA expression decreased in 2BS-p21a cells, which were more sensitive to apoptosis induced by NaBu. These results indicated that the expression amount of p21(WAF1) in 2BS cells was negatively related with its susceptibility to apoptosis induced by NaBu.