Micelle to solvent stacking was implemented for the recently established NACE-C4D method to determine tamoxifen and its metabolites in standard samples and human plasma of breast cancer patients. For stacking, the standard samples and extract after liquid-liquid extraction (LLE) were prepared inmethanol and the resulting sample solution was pressure injected after a micellar plug of SDS. Factors that affected the stacking such as SDS concentration, micelle, and sample plug length were examined. The sensitivity enhancement factor (peak height from stacking/peak height from typical injection of sample in BGE) was 15-22. The method detection limits with LLE were in the range of 5-10 ng/mL, which was lower than the established method (where the LLE extract was also prepared in methanol) with reported method detection limits of 25-40 ng/mL. The intraday and interday repeatability were in the range of 1.0-3.4% and 3.8-6.5%, respectively.