We report on a method for direct measurement of site density of vertically-aligned carbon nanotubes (CNTs). Site density is an important parameter of vertically-aligned carbon nanotube forests for various applications. By freezing the CNT forests in a polymer matrix and exposing the CNT ends, we obtained the site density of vertically aligned multi-walled CNTs through SEM observation and particle counting. Site densities of multi-walled CNTs grown by two different CVD processes, ferrocene/xylene process and Fe-Al/ethylene process, were measured to be ∼10 tubes/Ým2 and ∼53 tubes/Ým2, respectively. The results of site density distributions indicate non-uniform growth of carbon nanotubes at the micrometer scale in both processes.