NOVELTY - Iron-aluminum catalyst (I), is new.    USE - (I) is useful for preparing the carbon nanotube, which is useful as electrical conductive and strength enhanced filler in polymer composite material, thermal conductive and strength enhanced filler in metal composite, catalyst support of fuel cell, support material of organic process catalyst, storage material for methane and hydrogen gas, electrode material of lithium secondary battery, conductive material of lithium secondary battery, electrode material for high capacity electric double layer capacitor, field emitting material for display, and membrane material (all claimed).    ADVANTAGE - (I) is produced by the simple process excluding a hydrogen reduction step. The process produces the carbon nanotubes in high yield with high purity and in an economical manner by using (I).    DETAILED DESCRIPTION - Iron-aluminum catalyst of formula ((Fe1a:Al1b):My:Mg1z) (I) is new.    Fe1 = catalytic metal of Fe, or its oxide or derivative;    Al1 = catalytic metal of Al, or its oxide or derivative;    Mg1 = inactive support of Mg, or its oxide or derivative;    M = at least one transition metal comprising Co, Ni, Cr, Mn, Mo, W, V, Sn, Cu or their oxide or derivative;    x = 2-8;    y = 0-2.5;    z = 0.5-8, where x+y+z is 10, and x, y, and z are molar fractions of (the sum of Fe1 and Al1), M, and Mg1;    a = 2-5.5; and    b = 4.5-8, where a+b is 10, and a, and b are molar fractions of Fe1 and Al1.    INDEPENDENT CLAIMS are included for:    (1) the preparation of (I);    (2) preparing carbon nanotube comprising preparing the catalyst composition, supplying mixed gas of hydrogen and at least one carbon source comprising optionally saturated 1-4C hydrocarbon to the reactor at 500-900 degrees C, and growing and synthesizing carbon nanotube by decomposition of supplied carbon source on the surface of a catalyst composition according to a thermal chemical vapor deposition method; and    (3) a carbon nanotube having diameter of 5-20 nm and aspect ratio of 100-10000 prepared by the process.