Since ovarian cancer cells express CD44, which causes very strong cell adhesion to peritoneal mesothelium and an unfavourable prognosis, we designed small interfering RNA (siRNA) targeting the CD44 gene to analyse the functional consequences of this inhibition in human ovarian cancer. We transfected ovarian cancer cell line SKOV-3 with well-designed CD44 siRNA or control siRNA. Western blot analysis was used to assess the CD44 expression. Following stable transfection, significant inhibition of CD44 expression with 66.13 +/- 4.21 % (P < 0.05) in CD44 siRNA1 cells and 62.01 +/- 3.97 % (P < 0.05) in CD44 siRNA2 cells was detected. We performed in vitro experiments including cellular adhesion to hyaluronan and human peritoneal mesothelial cells, etoposide-induced apoptosis, and Boyden chamber invasion assays. The adhesion percentages of CD44 siRNA1 and CD44 siRNA2 cells were significantly lower than those of the control siRNA cells in adhesion both to hyaluronan and to human peritoneal mesothelium. The CD44 siRNA transfectants showed significant inhibition of in vitro invasion and loss of resistance to apoptosis than the control siRNA cells. In vivo study with BALB/c mice was applied to compare the tumour growth and peritoneal dissemination. Nude mice treated with CD44 siRNA cells revealed significantly lower tumour volume and less peritoneal dissemination compared to mice treated with the control siRNA cells. In conclusion, downregulation of CD44 expression by siRNA inhibits the in vitro adhesion, invasion and resistance to apoptosis of ovarian cancer cells, suppresses tumour growth and peritoneal dissemination of human ovarian cancer xenograft in nude mice.