^a College of Chemistry, Jilin University, Changchun, Jilin 130012, China 
^b Changchun Medical College, Changchun, Jilin 130031, China

Based on the sandwich immunoreaction and enlargement of colloidal gold, a simple spectrophotometric determination of human immunoglobulin G (IgG) was developed. The sandwich immunoreaction among the goat-anti-　human IgG, the human IgG and goat-anti-human IgG labeled with colloidal gold was completed on the surface of 96 well clear polystyrene high bind stripwell™ microplate. The immobilized colloidal gold was enlarged by the reaction of 0.01% HAuCl4 with 0.4 mmol•L－1 NH2OH•HCl. A common UV-Vis spectrophotometer was employed to measure the absorption of the colloidal gold enlarged. The absorption signal of colloidal gold is proportional to the logarithm of human IgG concentration ranging from 5.0×10－9 to 2.0×10－5 g•mL－1, which is comparable with those obtained by other immunoassays. In the proposed method, the immobilized colloidal gold can be easily enlarged and a new absorption band is present at about 620 nm, which makes the signal be recorded with a common medical analyzer. This spectrophotometric determination can be made in a common laboratory without the well-trained technician and the special equipment.