Decreased expression of the tumor suppressor gene, KAI1, is associated with metastasis formation in pancreatic cancer. The aim of the present study was to investigate whether KAI1 influences pancreatic cancer cell growth and colony formation. A full-length KAI1 cDNA expression vector was stably transfected into Panc-1 and MiaPaCa-2 pancreatic cancer cell lines. Transfection was confirmed by Western blot analysis and immunohistochemistry. Tumor cell growth and cell cycle distribution were determined by MTT cell growth assays, colony formation assays, and flow cytometric analysis. KAI1-transfected, but not control-transfected pancreatic cancer cells displayed cytoplasmic KAI1 immunoreactivity. Cell proliferation decreased in the KAI1-transfected cells compared to parental and control cells together with a Go/G1-phase cell cycle arrest. Colony formation was reduced by 2.6- and 3.5-fold in the KAI1-transfected Panc-1 and MiaPaCa-2 pancreatic cancer cells, respectively, compared with parental cells. KAI1 blocks pancreatic cancer cell growth through cell cycle arrest and inhibits anchorage-independent cell growth. These findings support the premise that KAI1 functions as a tumor suppressor in this malignancy.