H13 is a typical high-performance tool steel, and has a wide application in the mold making industry. To optimize mechanical properties of additively manufactured H13, a detailed investigation on tempering was conducted at 600 C and 700 C. Tensile testing, transmission electron microscopy (TEM) and atom probe tomography (APT) were utilized in the present study. It was found that the selective laser melted H13 showed unsatisfactory tensile properties in the as-printed condition, especially in terms of the elongation at fracture (~2.42%). After tempering at 600 C, the tensile properties, including the ultra-high yield strength (1483 ± 48 MPa), ultimate strength (1938 ± 62 MPa) and ductility (~5.8%), were significantly improved, which was attributed to the strengthening effect mainly from the presence of a large number of fine VC precipitates and the high density of dislocations. After tempering at 700 C, the material showed a high ductility (~10.95%) and moderate tensile strength (1076 ± 21 MPa). The fracture mode was a mixed ductile-brittle fracture for the specimen after tempering at 600 C, and became a ductile fracture for the specimen after tempering at 700 C. It is clarified that a transition in the microstructure explains the difference in the mechanical behavior between the specimens tempered at 600 C and 700 C. The present study provides a basis for manipulating the SLM-fabricated H13 for applications requiring either high strength or high ductility.