p21/WAF1 (p21) inhibits the activity of the cyclin/cdk complex and controls the G1 to S cell phase transition. In the present study, we used a recombinant adenoviral approach and gene gun technology to introduce p21 into esophageal cancer cells in order to assess the effect of p21 on cell growth. Infection with the p21 adenovirus (AdV) using gene gun technology resulted in inhibition of TE9 and KE3 cell growth. The levels of involucrin, which is a marker of squamous epithelium differentiation, markedly increased at 48 h and 72 h after p21 AdV infection in TE9 cells. These results indicate that p21 plays an important role in esophageal cancer cell proliferation. Overexpression of the p21 gene can inhibit cell growth and induce differentiation in esophageal cancer cells. p21 gene therapy may prove beneficial in the treatment of esophageal cancer.