A method for manufacturing isotope-doped carbon nanotubes (10) includes the steps of: (a) providing a carbon rod (209), the carbon rod including at least two kinds of carbon isotope segments (202, 203) arranged therealong according to need; (b) providing a laser beam source positioned opposite to the carbon rod; and (c) irradiating the carbon rod with a laser beam (214), wherein the carbon isotope segments of the carbon rod are consumed sequentially to form the isotope-doped carbon nanotubes. Growth mechanisms of the isotope-doped carbon nanotubes manufactured by this method can be readily studied.