Abstract: Boron-doped carbon nanotubes (CNTs) were prepared on porous silicon substrate by electron cyclotron resonance-chemical vapor deposition (ECR-CVD), with CH4, B2H6 and H2 used as source gases and Fe3O4 nanoparticle as catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, microstructure and composition of specimens. Comparing with the undoped CNTs, the boron-doped ones show the change in not only the morphology of CNT films, i.e., from high-orientability and intensive to low-orientability and scattered arrangement, but in the microstructure of CNTs, i.e., from hollow to bamboo-like tubes with bigger outer diameters, thicker tube wall and rough surface. Thus, the growth rate of boron-doped CNTs is lower than that of undoped CNTs.