OBJECTIVE To determine the content of thymosin alphal 1 in thymopeptide.METHODS High Performance Capillary electrophoresis (HPCE) analysis method was used at 25℃,using thymosin alphal 1 as the standard reference.The separation was performed on a 78 cm×30 μm uncoated sillica capillary column with the voltage 15 kV.The electrophoresis solution was 0.05 mol·L^-1phosphate buffer (pH 7.0).The sample was detected with a UV-detector at 200 nm.RESULTS The linearity was obtained over the range of 50～80 μg·ml^-1.The average recoveries of the check sample at the low,middle and high concentrations were 87%,91% and 97%,respectively.The mass content of thymosin alpha1 in 3 lots of thymopeptide solution were 1.24%,0.812% and 0.732% respectively.CONCLUSIONS The method could be used to determine the content of thymosin α-1 in thymopeptide for quality control.