Early pregnancy results in th production of various signal molecules such as steroids, prostaglandins, and many protein factors. The proteins especially produced by the placenta have been used to detect pregnancy for many years in other species. More recently, pregnancy-specific protein B, which is a placental glycoprotein can be measured by RIA or proteomic methods in serum of pregnant cow. And 2D Fluorescence difference gel electrophoresis (DIGE) is an emerging technique for comparative proteomics, which improves the reproducibility and reliability of differential protein expression analysis between samples. For this reason, we are analyzed serum of bovine. The purpose of this study was to apply DIGE technique for identification of bovine pregnancy-specific proteins using bovine pregnant and non-pregnant serum samples. Serums of 2 pregnant Holstein dairy cattle at day 21 after AI and those of 2 non-pregnant were used in this study. The molecular weight and charge matched cyanine dyes enable pre-electrophoretic labeling of non-pregnancy and pregnant serum proteins which are then mixed and labeled with Cy2 were used as an internal standard. Two pools of proteins are labeled with Cy3 and Cy5 fluorescent dyes, respectively. Labeled proteins with Cy2, Cy3 and Cy5 mixed together and separated in same gel and then were detected by fluorescence image analyzer. The 2D DIGE analysis using fluorescence CyDye flour showed higher sensitivity and better reproducible results than conventional 2D gel electrophoresis. Approximately 1,500 protein spots were detected by 2D DIGE. The differentially expressed proteins were identified by MALDI-TOF Mass spectrometer. Total 16 protein spots differentially expressed in the pregnant serum were detected, among which 7 spots were up-regulated proteins identified as conglutinin precursor, modified bovine fibrinogen, IgG1 etc, and 6 spots were down-regulated proteins identified as hemoglobin, complement component 3, bovine fibrinogen, IgG2a etc. These results indicated that DIGE system could be advantageous for the analysis of serum proteomics diversified by physiological conditions.