Separations of neurotransmitters such as dopamine (DA), ser otonin (5-HA), norepinephrine (NE) and epinephrine (E) were performed successf ully using a homemade electric field modulated capillary electrophoretic system, which could offer both radial and axial electric fields with only one high volt age power supply. DA and 5-HT were eluted simulaneously and could not be resolv ed in 0.01 mol/L phosphate buffer at pH 2.5. Alcohol additives, such as methanol , ethanol or 1-propanol were added to the buffer to change the solvation shell of the solutes, which changed their effective sizes and electrophoretic mobiliti es of the solutes accordingly. The optimum composition was a buffer of 20% (V ／V） 1-propanol, with resulted resolutions 0.74 (DA/5-HT), 0.56(5-HT/NE) and 0.77 (NE/E). If a positive radial voltage of 6.6 kV was applied, the resolut ions were improved to 1.48, 0.71 and 1.32, respectively.