The method of serum gamma-glutamyl transferase colorimeter assay was modified by changing the wave length from 420 nm to 400 nm, the incubated temperature from 37 degrees C to 50 degrees C, the sample amount from 30 microliters to 6 microliters. The modified method was proved to be more sensitive, with CV of intra-group being 2.06% and accuracy 97.4%. The method is suitable for clinical application with small-amount blood samples collected from earlobe or finger tip.