During the process of sodium butyrate (NaBu)-induced apoptosis in 2BS cells, p21^WAF1 gene expression decreased obviously and gradually,bcl-2 gene expression did not decrease until apoptosis happened, c-myc and c-fos genes expression enhanced, while p53 and HER-2 genes expression had no obvious change. To analyze the change of p21^WAF1 promoter activity, 2BS-WP cells were used, which were stabely transfected with pDOR-WPs that containing different length of p21^WAF1 promoter followed by green fluorescence protein (GFP) report gene. The results showed that the level of GFP expression decreased during NaBu induction, and the main regulating region was 0～－800 bp at upstream of TATA box of p21^WAF1 promoter. It is suggested that down-regulation of p21^WAF1 promoter activity was involved in the process of NaBu-induced apoptosis in 2BS cells, which was possibly p53-independent.