In this work, a characterization in terms of microstructural and mechanical properties of IN718 additively manufactured lattice structures has been performed, with a comparative study between as built and heat-treated samples. All samples have been produced through L-PBF technique. The heat treatment consisted in a solution annealing, followed by a first ageing at 720 °C and a second ageing at 620 °C. The work is aimed at studying structural, microstructural and mechanical properties of three different lattice structures: diamond (A), body diagonals (B) and rhombic dodecahedron (C), with relative densities of 30%, 50% and 30%, respectively, before and after the heat treatment. In as-built lattice structures, the microstructure shows elongated melt pools on xy plane (perpendicular to growth direction), while on xz plane (parallel to growth direction) melt pools assumed an arc shape, due to the presence of a thermal gradient. Overall, a fine cellular/dendritic microstructure was observed, constituted by the strengthening γ’/γ’’ phases, indicative of a very high thermal gradient and an intermediate solidification rate, with equiaxed and elongated grains on xy and xz planes, respectively. Concerning compressive behaviour, the stress-strain curves of lattice structures A and C showed a stress plateau, suggesting a bending dominated behaviour, while lattice structure B did not show such a feature and revealed larger values of elastic modulus and yield stress, as consequence of its higher density. After the heat treatment, the overall shape of the grains, both along xy and xz planes, remained unaffected with respect to that of as-built samples. Inside the grains, some fine γ’/ γ’’ precipitates were dispersed in the γ matrix, while along the grain boundaries coarser precipitates were continuously distributed. From EBSD analyses, these can be attributed to both δ and Laves phases. From Vickers hardness measurements, it turned out that the average hardness values were higher than those of as-built samples and the standard deviation was smaller, probably correlated to a homogenization deriving from the heat treatment. The elastic modulus almost doubled for all the structures, while for lattice A and B the behaviour in the plastic regime showed small fluctuation, probably referred to the rupture of the struts of the lattice structures. On lattice structure A, the fracture occurred along the (111) direction, showing features of both brittle and ductile behaviours. The embrittlement of the lattice structures was related to the large presence of pores and of both Laves and δ phases along the grain boundaries.