The layered ternary copper sulfide alpha BaCu4S3 showed a peritectic-like decomposition at 816-911 K, in contrast to the earlier report. Electrical resistivity rho and differential scanning calorimetry (DSC) measurements showed a phase transition at 188-205 K, which was associated with a sharp increase of rho on cooling. The electron diffraction studies revealed that the transition was accompanied by the superlattice formation with a wave vector of q = (1/5)b*. The transition is possibly associated with a positional order-disordering or a charge-density-wave formation. It was proposed that the relatively high conductivity originates from atomic vacancies.