In order to improve the sensitivity of CE-ESI-MS for the analysis of brain-gut peptides, a solid-phase extraction combined with field-amplified sample injection was used for the pre-concentration of the brain-gut peptides. Compared with the conventional pressure injection method, the sensitivity in the detection of brain-gut peptides was improved more than 100-fold. The possible factors affecting sample stacking, such as the sample matrix, the composition and the length of the water column, the types and the volumes of eluent, have been investigated in detail. Under the optimum conditions, the detectable concentration of brain-gut peptides was found to be as low as 0.02 mu M. A linear response concentration for the detection was developed in the range of 0.08-25 mu mol/L. A real sample of human cerebrospinal fluids, which was spiked with brain-gut peptides, was also examined in order to evaluate the reliability of the proposed approach. The recovery of the method was in a range from 69.2 to 85.4%. The method was found to be reliable, accurate and potentially applicable for clinical drug analysis.