AbstractLignin graft copolymer (LGC) was prepared using an addition polymerization technique that involved grafting a 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomer onto soda lignin (SL). The optimal polymerization conditions were found to be as follows: soda lignin, 2.0 g; initiator, 3% (w/w) potassium persulphate of SL; mass ratio of AMPS to SL, 1:2; reaction time, 7 h; and reaction temperature, 60 °C. The LGC was characterized using a Fourier transform infrared (FTIR) spectroscopy, a thermogravimetric analyzer (TGA), and gel permeation chromatography (GPC). The filtrate loss controlling ability of the LGC was evaluated using the American Petroleum Institute Recommended Practice 13-B 1 standard procedures. The results showed that the LGC has remarkable rheological and filtration controlling properties at both room temperature and high aging temperatures (190 °C).