<p>The present research was conducted on corpora lutea (CL) samples of healthy buffaloes (<i>n</i> = 24) with the aim to localize presence of immune cell macrophage, immunohistochemically and ultrastructurally. The collected CL were categorized into four different stages i.e., early (stage I, 1 to 5 days, <i>n</i> = 6), mid (stage II, 6 to 11 days, <i>n</i> = 6), late luteal phase (stage III, 12 to 16 days, <i>n</i> = 6) and regressing phase (stage IV, 17 to 20 days, <i>n</i> = 6), based on their gross morphology. The macrophages were observed occasionally throughout the luteal parenchyma of early and mid-luteal CL. However, their number was lowest during early and mid-luteal phases being 7.7 ± 0.98 (Mean ± S.E) and 6.37 ± 0.79 per unit area, respectively. The number was considerably higher in regressing phases i.e., late luteal phase (60.45 ± 4.39 per unit area) and corpus albicans (108.25 ± 6.35 per unit area). Ultrastructurally as well, their presence was observed to be higher in the regressing phases as cells with filopdia for the process of phagocytosis. These findings concluded that the presence of macrophages, although lower in early and mid-luteal phases of CL formation, indicated their probable role in promoting angiogenesis and thus proliferation of buffalo CL during its formation. However, their considerable higher presence during late and regressing phases of CL led to increased phagocytosis of degraded luteal cells that thereby promoted its structural luteolysis.</p>