A novel fibrous composite of platelet carbon nanofibers-silica fiber (PCNFs-SF) was synthesized via acetic acid steam reforming (ASR) and then employed as a support for a Co catalyst in the ASR. For comparison, the catalytic behavior of cobalt (Co) catalysts supported on carbon nanotubes-silica fiber (CNTs-SF), silica fiber (SF) and porous silica (Q10) was also studied. The characterization by field emission scanning electron microscopy and transmission electron microscopy analyses demonstrated that the PCNFs-SF was like graphite stacked platelets. Both PCNFs-SF and CNTs-SF composite supports enhanced the dispersion of metallic cobalt to achieve smaller Co2O3 particle sizes and strengthen the metal-support interaction. Consequently, the Co/PCNFs-SF and Co/CNTs-SF composite catalysts afforded a higher ASR catalytic activity and selectivity towards hydrogen production than that of the Co/SF and Co/Q10 catalysts. The presence of the carbon nanostructure in the catalyst composites was also found to improve the long-term stability in ASR. The activity of the Co/PCNFs-SF and Co/ CNTs-SF composite catalysts remained stable all times during a 12 h stability test. The strong interaction between metal and support together with the unique structure of PCNFs-SF and CNTs-SF composites could effectively suppress deactivation of the catalysts in ASR.