Methods are provided for aligning carbon nanotubes and for making a composite material comprising aligned carbon nanotubes. The method for aligning carbon nanotubes comprises adsorbing magnetic nanoparticles to carbon nanotubes dispersed in a fluid medium to form a magnetic particle-carbon nanotube composite in the fluid medium; and exposing the composite to a magnetic field effective to align the nanotubes in the fluid medium. The method for making a composite material comprising aligned carbon nanotubes comprises (1) adsorbing magnetic nanoparticles to carbon nanotubes to form a magnetic particle-carbon nanotube composite; (2) dispersing the magnetic particle-carbon nanotube composite in a fluid matrix material to form a mixture; (3) exposing the mixture to a magnetic field effective to align the nanotubes in the mixture; and (4) solidifying the fluid matrix material to form a nanotube/matrix material composite comprising the aligned nanotubes which remain aligned in the absence of said magnetic field.