Extensive branching morphogenesis takes place during pregnancy in the mammary gland. It is accompanied by the rapid proliferation of the Mammary Epithelial Cells (MECs). To gain insights into the proteomic changes that occur during the proliferation of MECs from buffalo (Bubalus bubalis) origin, we explored the deep proteome profile of buffalo mammary epithelial cells (BuMECs) using mass spectrometry (MS). To achieve this, we employed the sub-cellular fractionation approach and secretome analysis. Proteins were isolated separately from four subcellular fractions (SCFs) containing cytosolic (SCF-I), membranous and membranous organelle’s (SCF-II), nuclear (SCF-III) and cytoskeletal (SCF-IV). These sub-cellular specific protein fractions were processed using in-solution digestion and analyzed with nano-LCMS/MS. The MS analysis identified 8330, 5970, 5288 and 4818 non-redundant proteins in the fractions SCF I, II, III and IV respectively. To evaluate the secretory proteins in these cells, gel-based proteome approach was used which revealed a total of 792 non-redundant proteins. Altogether, combined analysis of all the five fractions including four sub-cellular fractions and secretome resulted in the identification of 12,609 non-redundant proteins. A total of 325 molecular pathways were identified after extensive analysis. The most enriched pathways associated with these proteins were metabolic, PI3-AKT, MAPK, mTOR, Insulin, estrogen and Oxytocin signaling. Our study demonstrated for the first time highest number of proteins identified by MS in any cell types including MECs.