p38 mitogen-activated protein (MAP) kinase α (p38α) is a broadly expressedsignaling molecule that regulates a variety of cellular processes. Most studies of p38α have been in differentiated somatic cells. In this study, we investigated the roles of p38α in the regulation of embryonic stem (ES) cell activities using ES cells isolated from p38 knockout mouse embryos (p38α −/ −ES cells). We report here that p38α −/ −ES cells displayed several altered features different from wild type cells. p38α −/ −ES cells have significantly increased cell adhesion capacity to several extracelluar matrix proteins, correlating with elevated phosphorylation of focal adhesion kinase and paxillin. Deletion of p38α results in increased cell viability, correlating with increased expression of survivin and activation of AKT, two molecules that are known to improve cell viability. p38α −/ − ES cells consistently reach confluence faster than wild type cells in routine cell culture. However, this is not due to a higher cell proliferation rate in p38α −/ − ES cells as judged by cell cycle analysis, but rather is likely a result of improved cell adhesion and/or cell viability. The results in this study revealed some novel functions of p38α that were not previously reported in differentiated cells. p38α regulates cell morphology, proliferation, and survival, but it may operate through similar as well as unique regulatory mechanisms in somatic cells and ES cells. This work was supported by a grant from the National Institutes of Health (R15HL081126) and a Faculty Summer Research Grant from the University of Southern Mississippi.