The effect of Ag buffer layers epitaxially grown on Si(111) substrates on the growth of carbon nanotubes (CNTs) has been investigated. We have examined the morphology of Co particles deposited on the epitaxial Ag layer and SiO2, and that of CNTs grown on the epitaxial Ag layer and SiO2. In this study, the epitaxial Ag buffer layer was stable during CNT growth. The density of Co particles on the epitaxial Ag layer was higher than that on SiO2 and the mean diameter of Co particles on the epitaxial Ag layer was smaller than that on SiO2. Furthermore, the diameter distribution of Co particles on the epitaxial Ag layer was narrower than that on SiO2. According to these results of diameter distribution of Co, the density of CNTs grown on the epitaxial Ag layer was higher than that on SiO2. From these results, the epitaxial Ag layer is suitable as an electrode of a CNT device.