Abstract: To understand the effect of glutamic acid (Glu) on the binding mechanism between food additive bright blue (BB) and the carrier protein, the interaction mechanism between BB and bovine serum albumin (BSA) in the presence of Glu were studied considering binding force, binding distance, binding site, and protein conformational change. The experimental results showed that BB quenched the endogenous fluorescence of BSA via static quenching. However, the fluorescence quenching constant of BB towards BSA decreased from (8.31±0.52)×10⁴ L·mol⁻¹ to (5.43±0.04)×10⁴ L·mol⁻¹ in the presence of Glu, and the binding constant decreased from (1.35±0.04)×10⁵ L·mol⁻¹ to (3.81±0.20)×10⁴ L·mol⁻¹ (at 313 K), indicating that Glu weakened the binding of BB to BSA. Additionally, Glu also shortened the binding distance between BB and BSA (from 3.49±0.02 nm to 3.45±0.04 nm) and reduced the alteration of BSA's secondary structure by BB (the α-helix content changed from 36.09%±0.01% to 42.14%±0.01% (when the BSA-Glu-BB was 1:20:1)), indicating that Glu partially prevented the conformational disturbance of BSA by BB.