Development of mouse fetus brains can be defined morphologically and functionally by three developmental stages, embryo day (ED) 16, postnatal stage one week and eight weeks. These defined stages of brain development may be closely associated with differential gene expression rates due to limited cellular resources such as energy, space, and free water. Complex patterns of expressed genes and proteins during brain development suggests the changes in relative concentrations of proteins rather than the increase in numbers of new gene products. This study was designed to evaluate early protein expression pattern in mouse fetus brain. The mouse brain proteome of fetus at ED 15.5, and 19.5 was obtained using 2-dimensional gel electrophoresis (DE). Analysis of the 2-DE gels in pH 3-10 range revealed the presence of 15 differentially expressed spots, of which 11 spots were identified to be known proteins following MALDI-TOF analysis; 3 spots were up-regulated and 8 spots were down-regulated in the mouse fetus brain at ED 15.5. UP-regulated proteins were identified as MCG18238, isoform M2 of pyruvate kinase isozymes M1/M2, isoform 2 of heterogeneous nuclear ribonucleoprotein K, heterogeneous nuclear ribonucleoprotein H2, creatine kinase B-type, 40S ribosomal protein SA and hemoglobin subunit beta-H1. Down-regulated proteins were putative uncharacterized protein, lactoylglutathione lyase and secreted acidic cysteine rich glycoprotein. Our results revealed composite profiles of mouse fetus brain proteins related to mouse fetus development by 2-DE analysis implying possible roles of these proteins in neural differentiation.