In article the experimental assessment ofpossibility of decrease in gas permeability of a composite material on the basis of matrix modifying by carbon nanotubes that is important for effective work of high-pressure tanks is given. The technique of carrying out tests of gas permeability of a composite and manufacturing techniques of examinees of samples is described. The technique ofprocessing of results of experiments is given. It is shown that matrix modifying by carbon nanotubes reduces gas permeability of a composite more than by 30%.