In response to the increasing demand for reliable performance of nickel-based superalloy components in recent years, this study focused on a GH4099 superalloy fabricated via selective laser melting to investigate the anisotropy in its microstructure and mechanical properties. The microstructure of the as-deposited GH4099 alloy was characterized via OM, SEM and EBSD, and tensile tests were conducted at room temperature in both the horizontal and deposition directions to investigate the relationships between the microstructure and mechanical properties. The experiment reveals that the as-deposited sample consists of columnar crystals that epitaxially grow along the deposition direction, with a small amount of small carbides present but no second phase precipitation. The yield strength and fracture strength in the horizontal direction are both greater than those in the deposition direction, but the elongation is lower. The fracture surfaces in both directions exhibit typical transgranular fracture morphologies.