Sum rule calculations for the integrated bremsstrahlung-weighted cross-section σb for6Li have been performed with resonating-group wave function in a single channel of alpha and deuteron substructures. The r.m.s. radius of6Li has been also calculated. A reasonable value of σh below pion threshold has been obtained using no adjustable parameters if the lack of space symmetry in the ground-state wave function of6Li is taken into account. The intercluster exchange of particles is shown to be rather important.