To determine the adulteration of soybean proteins in dairy product, a microchip-CE device was developed to isolate selected fraction of soybean and milk proteins in pI range from 5.5 approximate to 7.0 by 1D IEF, followed by ITP/CZE in the embedded capillary for preconcentration, separation and UV detection at 280 nm. Compared to IEF-CZE without ITP preconcentration, the enhancement factor (EF) in detection of soybean proteins was 20times. Adulteration of 0.1% soybean protein in total dairy proteins can be detected in less than 10 min.