In the present study, the effect of various processing parameters is investigated for building Al2O3 ceramic structures by laser additive manufacturing using the direct energy deposition technique (LAM-DED). The study shows that uniform single tracks and three dimensional (3D) structures of Al2O3 can be fabricated on alumina and Ti–6Al–4V substrates at the laser power of ~225 and ~300 W, respectively, for a fixed scanning strategy (θ = 0°), feed rate (8 g min-1) and scanning speed (0.6 m min-1). Optical microscopy, synchrotron-based X-ray micro-computed tomography (SR-μCT) examination and density measurement reveals that the bulk Al2O3 structures built on Ti–6Al–4V substrate have lower defects (porosity and cracks) and higher relative density (RD) = 85% than that fabricated on the alumina substrate (RD = 70%). This is primarily attributed to uniform melt pool formation on Ti–6Al–4V substrate at higher laser power. In addition to laser power, it is also found that the thermo-physical properties of the substrate material play a vital role on melt pool formation, which in turn decides the defect structure in built bulk Al2O3 components. Further, the change in scanning strategy to 45° and 67° increases the density of bulk Al2O3 structures built on Ti–6Al–4V substrate to 90% and 95%, respectively. The SR-μCT analysis of bulk structures built with different scanning strategies on the Ti–6Al–4V substrate confirmed that scanning strategy plays a vital role in the shape, size, and distribution of pores that formed during LAM-DED process. The study paves a way for LAM-DED of Al2O3 bulk structures by deriving the advantage of scan strategy and optimized processing parameters.