Using density functional theory with the generalized gradient approximation, we have studied the structures of small (BaO)(n) (nless than or equal to9) clusters. We find that there are three different growth modes (cubic-like, ring-like and anti-tetragonal prism based) for the (BaO)(n) clusters. Although the cubic-like structure is prevailing for the clusters, the energy difference from other growth modes is small. The anti-tetragonal prism based structures are found to be ground states for (BaO)(5) and (BaO)(7).