In polyethylene glycol 2000 (PEG)-(NH4)2SO4-edible pigment two-phase aqueous systems, the spectroscopic behaviour of the complexes of edible pigment and human serum albumin in PEG phase was investigated. Effects of different acidity, quantities of PEG and salt, reaction time, and coexistent matter on the determination of systems were discussed. Experimental results show that compared to BS spectra, the maximum wavelength of the complex of human serum albumin shifted to the red by 13 nm in buffer solution at pH 8, the maximum binding number of 40 was measured by molar ratio method, and the apparent molar absorptivity was 9.4 x 10(4) L x mol(-1) x cm(-1). The linear range was 0-21.07 mg x L(-1). With different surfactant, the interaction mechanism of protein and edible pigment was discussed.