Syndecan-4 (S4) is a cell membrane-associated heparan sulfate proteoglycan that forms oligomers in muscle satellite cells. The S4 oligomers activate protein kinase Cα (PKCα) through the S4 cytoplasmic domain and may regulate the activation of ras homolog gene family member A (RhoA), a signal transduction molecule down-stream of PKCα which is thought to influence cell migration. However, little is known about the function of the S4 cytoplasmic domain in satellite cell migration and RhoA activation. The objective of the current study was to determine the function of S4 and its cytoplasmic domain in cell migration and RhoA activation. To study the objective, clones of S4 and S4 without the cytoplasmic domain (S4C) were used in overexpression studies, and small interference RNAs targeting S4 or RhoA were used in knockdown studies. Satellite cell migration was increased by S4 overexpression, but decreased by the knockdown or deletion of the S4 cytoplasmic domain. The RhoA protein was activated by the overexpression of S4, but not with the deletion of the S4 cytoplasmic domain. The treatment of Rho activator II or the knockdown of RhoA also modulated satellite cell migration. Finally, co-transfection (S4 overexpression and RhoA knockdown) and rescue (the knockdown of S4 and the treatment with Rho activator II) studies demonstrated that S4-mediated satellite cell migration was regulated through the activation of RhoA. The cytoplasmic domain of S4 is required for cell migration and RhoA activation which will affect muscle fiber formation.