The review highlights the in situ technique of the X-ray absorption spectroscopy (XAS) in the recent advances on understanding the structural features of solid catalysts used in the CO hydrogenation relevant to Fischer-Tropsch synthesis. The report is mostly concerned with mono- and bimetallic nanoparticles. The in situ XAS technique is applied for some examples illustrating the influence of the nature of the support on reducibility of Co-based mono- and bimetallic (Co-M where M = Pt, Ru or Re) systems. Based on the structural parameters a model is presented. The advantage and limitation of the X-ray absorption technique will also be discussed.