Phosphorous-modified gamma-Al2O3 support is used to prepare cobalt-based catalysts (CoP(x)Al, x = 0-4 wt%) for dry reforming of methane (DRM). From the studied catalysts, CoAl displays the highest conversions of CH4 and CO2 at the initial stage due to good cobalt dispersion. However, both conversions decrease significantly after 20 h on stream due to the formation of inactive CoAl2O4 phase through the reaction of oxidized CoOx with the alumina surface. For the CoP(x) Al catalysts, although the initial CH4 and CO2 conversions decrease gradually as the phosphorus loadings increased, all catalysts show more stable catalytic activity than the CoAl catalyst. Formation of aluminum phosphate (AlPO4) on the alumina surface can be achieved by the addition of phosphorus. The AlPO4 phase has the capacity to suppress the formation of CoAl2O4 phase. Phosphorous loadings on alumina surface of up to 1-2 wt% exerted positive effect on catalyst stability, whereas loadings above this threshold exerted opposite effect.