Commercially, multi-walled carbon nanotubes (MWCNTs) production methods are based on the use of transition metal catalysts such as chemical vapor deposition (CVD). Raw MWCNTs usually contain metal catalysts and other carbon impurities. A common route to eliminate these impurities is an acid treatment. In addition, this route induces cutting of MWCNTs which can control the aspect ratio of MWCNTs. The aspect ratio controlled MWCNTs can use many applications such as the electrode material, biological imaging and sensing, etc. In this study, the aspect ratio of MWCNTs was controlled using an acid treatment with a 3:1 concentrated H2SO4/HNO3 mixture by varying the treatment time. Results show that an acid treatment can control the aspect ratio of MWCNTs. The aspect ratio controlled MWCNTs were observed by TEM and Raman spectra.