CoCrFeMnNi high-entropy alloys containing 1 at% carbon (C-HEAs) were additively manufactured using selective laser melting (SLM). Superior tensile properties of the as-built C-HEA (to previously reported ones) were achieved by utilizing multiple strengthening mechanisms (i.e. solid solution, grain refinement, dislocation density, and nano-precipitation) by this new manufacturing method. In particular, the SLM process could allow to maximize the strengthening effect of carbon addition to HEAs via finely distributed nano-carbides at the boundaries of solidification cellular structure. This work will open a new window to utilize the SLM process for enhanced mechanical properties of HEAs with great potential. GRAPHICAL ABSTRACT IMPACT STATEMENT CoCrFeMnNi high-entropy alloys containing 1 at% carbon were successfully produced by selective laser melting, and the alloys exhibited much better tensile performance than additive manufactured high-entropy alloy previously reported.