Reaction cross sections of Li-8 on stable targets were measured at intermediate energies. With the existing experimental data of interaction cross sections at 790 MeV/nucleon the nucleon density distribution of Li-8 was extracted by the use of the modified Glauber model. Meanwhile, the existing data of B-8 have been also reanalyzed. Structures of Li-8 and B-8 were compared through the density. On the basis of dilute surface densities, the discussion of Li-7(n,gamma) Li-8 and Be-7(p,gamma) B-8 capture reactions was performed within the framework of the direct capture reaction mechanism. The calculations agreed quite well with the experimental data as well as other analyses.