3-Phosphoinositide-dependent protein kinase 1 (PDK1) is centrally involved in cancer progression, including proliferation, apoptosis and invasion. However, its expression pattern and possible cellular functions in human colorectal cancer remain unclear. In the present study, we show that PDK1 expression is up-regulated at both mRNA and protein levels in colorectal cancer clinical specimens and cell lines. Transient knockdown of PDK1 suppresses cellular growth, induces cellular apoptosis and causes abnormal cell cycle distribution. Meanwhile, decreased PDK1 level is closely associated with reduced Akt/cyclin D1 activity. Activating AKT activity and reintroducing cyclin D1 expression significantly compromised the oncogenic activity induced by PDK1. Together, our findings elucidate a key role for PDK1 in colorectal cellular functions trigged by the Akt/cyclin D1 pathway, thus providing a novel insight of PDK1 in colorectal carcinogenesis.