Biogas is a promising low-calorific fuel composed of 50-80% CH4 and 20-50% CO2 and provides numerous economic and environmental benefits. In this study, biogas combustion in a two-layer porous burner packed with spherical alumina beads was experimentally investigated to provide guidelines for biogas burner design. The equivalence ratios varied from 0.75 to 0.95 at four different CO2 content values (25, 30, 35, and 40%). The flame stability limits at various equivalence ratios and CO2 concentrations were obtained. The range of biogas equivalence ratios for stable flame was at a higher level than the range for pure CH4. The flame tended to move from the upstream to the downstream region as the flame speed increased, resulting in high exhaust gas temperatures. The effects of the biogas CO2 ratio on the flame temperature, pressure drop of reaction flow, and radiation efficiency were also examined in detail. The NOx, CO, and HC emissions and the flame speed at the four CO2 concentrations were also analyzed. The NOx concentration was below 12 ppm for both biogas and pure methane. The CO and HC emissions for biogas and pure CH4 in the sphere-packed bed were higher than pure CH4 in a foam burner at lower flame speeds (S < 40 cm/s). However, the emissions were almost identical and maintained constant values at higher flame speeds (S > 40 cm/s) for the two different kinds of burners.