Here we used the iron oxide nanoparticles derived from ferritin as catalyst for the synthesis of carbon nanotubes (CNTs) by the chemical vapor deposition (CVD) of coal gas. It has been found that the structure and morphology of CNTs can be tailored, to some degree, by varying the experimental conditions such as catalyst loading and process parameters. In addition to straight CNTs, some Y-branched CNTs were also obtained, which might be due to the sulfur species in the coal gas.