The effect of the polymer molecular weight on the catalytic properties of cobalt composites based on polyacrylonitrile (PAN) in the carbon monoxide hydrogenation reaction has been studied. It has been found that the CO conversion tends to 100% in the presence of any of the systems. It has been revealed that for the system based on PAN with a higher molecular weight, a quantitative CO conversion is observed at a lower temperature. It has been assumed that during the synthesis of the composite materials, the active phases undergo encapsulation differently. X-ray diffraction (XRD) analysis has revealed that the formation of metallic cobalt particles occurs regardless of molecular weight.