Our study demonstrated deposition of fully uniform amorphous boron carbide (B4C) thin films on carbon nanotubes (CNTs) by a conformal CVD process. No clustering or clogging at the pore sites are seen from STEM and SEM analysis. XPS, Raman spectroscopy and Electron diffraction measurement collectively show that the deposition of B4C films does not cause any structural modification to the CNT lattice, and it remains intact. The observed near-surface lattice matched interface and the amorphous growth towards the exterior prevent the introduction of residual stress during the film deposition. Image processing techniques affirmed the compatibility of the deposition process with the ability to precisely control the thickness, highlighting the tunability of pore sizes in the B4C deposition process. This conformal deposition process of B4C on CNTs within a membrane structure provides new possibilities to modify the properties of CNT membranes.