Microstructural modifications and mechanical properties of samples manufactured from conventional and nanocomposite WC/Co12 powders by means of Selective laser melting (SLM) are compared after processing with the same parameter set. Studying their homogeneity reveals that in both samples coarse and fine carbides segregate in the molten pool. X-ray diffraction (XRD) analysis shows significant changes in the microstructure and crystalline phases present in the WC/Co mixture and after SLM. Thermal decomposition of WC leads to the formation of W2C dicarbides and the appearance of the complex Co-W-C ternary phase. No residual pure cobalt after SLM was detected in the samples. The Williamson-Hall method allows determining coherent WC domain sizes of conventional and nanostructured powders (56 +/- 6nm and 10 +/- 3nm, respectively) and microstrains (approximate to 0 for both) as well as their modifications after SLM processing (180 +/- 50nm and 210(-3)+/- 410(-4) for the nanophased sample, and 330 +/- 100nm and 210(-3)+/- 410(-4) for the conventional one, respectively). The microhardness of the part produced from the nanophased powder is slightly increased in both the coarse (approximate to 1496 HV0.3) and fine (approximate to 1542 HV0.3) carbide segregation regions compared to the sample obtained from the conventional powder (1384 HV0.3 and 1515 HV0.3 for coarse and fine regions, respectively).