Skeletal myogenesis is a multistep process that involves cell cycle exit, expression of muscle-specific genes and formation of multinucleated myotubes. Growth arrest specific gene 1 (Gas1) is a GPI-linked membrane protein and originally identified as a growth arrest-linked gene in fibroblasts. Promyogenic cell surface protein, Cdo functions as a component of multiprotein complexes that include other cell adhesion molecules, like Cadherins to mediate cell contact signaling. Here we report that Gas1 and Cdo are coexpressed in muscle cells and form a complex in differentiating myoblasts. Interestingly, Cdo(-/-) myoblasts display defects in Gas1 induction during differentiation. Overexpression or depletion of Gas1 enhances or decreases myogenic differentiation, respectively. During myoblast differentiation, Gas1 depletion causes defects in downregulation of Cdk2 and Cyclin D1 and up-regulation of miR-322, a negative regulator of Cdk2 activities. Furthermore overexpression or knockdown of Gas1 either enhances or decreases activation of p38MAPK that functions downstream of Cdo. Additionally, Gas1 overexpression in Cdo-depleted C2C12 cells restores p38MAPK activities and differentiation abilities. These data suggest that Gas1 promotes myogenic differentiation through regulation of cell cycle arrest and is critical to activate p38MAPK, most likely via association with Cdo/Cadherin multiprotein complexes.