Humic acid (HA) is a natural adsorbent and has special physical and chemical characteristics that form the foundation for disposal of pollutants from a combustor flue gas. HA, which occurs widely in soil, water, and low-rank coals, has already been proposed as a candidate that can be used as a sorbent for air pollution control. A flue gas desulfurization and denitrification (FGDD) process employing HA seems like a promising approach. It is a better choice using HA-Na as a desulfurization additive to improve wet limestone scrubbers or other FGDD processes. This paper reviews the recent development of waste gas treatment by HA with special reference to HA for removal of SO2, NOx, CO2, H2S, and heavy metals.