We report on the simultaneous sub-Doppler laser cooling of 6 Li and 7 Li isotopes using gray molasses operating on their respective D 1 atomic transitions. For 7 Li we show that the sub-Doppler cooling can be achieved with two distinct-type transitions, where the upper level can be either of the two 2 2 P 1/2 hyperfine states. We obtain temperatures of ∼85 μK, with atom numbers of ∼10 8 , and phase-space densities in the range of 10 −6 −10 −5 for both isotopes. These conditions provide a good starting point for loading the mixture into an optical dipole trap and performing evaporative cooling to quantum degeneracy. Our work provides a valuable simplification for the preparation of ultracold 6 Li-7 Li mixtures, which were proven to be a successful system for the study of impurity physics and Bose-Fermi superfluids.