The structure and dispersion of the active phase present in sulfided Mo/C and Co-Mo/C catalysts are studied by means of Mo K-edge EXAFS. EXAFS measurements were carried out at liquid N2 temperature on freshly sulfided catalysts in situ. Due to a high signal-to-noise ratio of the experimental data, detailed information about the structural parameters of the active phase can be obtained. The Mo/C and Co-Mo/C catalysts consist of very small MoS2-like particles, which contain on average 5 to 6 Mo ions (Mo/C), and 7 to 8 Mo ions (Co-Mo/C). There are indications for the presence of a Mo-C interaction in Mo/C and Co-Mo/C. The Mo-C coordination distance is estimated to be 1.9 ± 0.1 Å. There are also indications for the presence of a Mo-Co interaction. The Mo-Co coordination distance was estimated to be 2.8 ± 0.1 Å.