In this work, the local atomic level composition of BAlN films with 20% B was investigated using atom probe tomography. Dislocations and elemental clustering were confirmed along which Al atoms tend to segregate. The presence of local compositional heterogeneities (dislocations and small clusters) and impurities is related to the variation of local alloy stoichiometry of the BAlN films. The roughness and interface abruptness of BAlN/AlN were investigated, and a few nm of B and Al composition gradient in BAlN adjacent to the interface was observed. The nanoscale compositional analysis reported here will be crucial for developing BAlN films with a high B content and larger thickness for future high power electronics and optical applications.