In pH 7.0 Tris-HCl buffer solution, goat-anti-rabbit IgG is combined with rabbit IgG specifically, and aggregates to form immune complex particles that exhibit three resonance scattering peaks at 330, 400 and 520 nm respectively, and a synchronous scattering peak at 470 nm, in the presence of PEG-20000. The scattering intensity at 470 nm is linear to the rabbit IgG concentration in the range of 1.33 to 133.3 microg x mL(-1). The detection limit is 0.99 microg x mL(-1). The method was applied to the quantitative analysis of rabbit IgG, with satisfactory results.