Introduction <p> Chronically elevated proinflammatory cytokines and following low-grade tissue inflammation in adipose tissue of patients with obesity induced by M1 macrophages may increase insulin resistance and type 2 diabetes. However, actual macrophage distribution in patients with obesity and diabetes has not clearly confirmed yet. We aimed to reveal the relationship of macrophage accumulation and polarization in visceral fat to patients’ obesity and diabetes status, and to validate the role of preoperative M1 macrophage polarization as a predictor for diabetic remission after bariatric surgery.</p> Methods <p> This single-center prospective observational study enrolled 80 patients. Experimental and control 1 group included patients with BMI≧30, with/without type 2 diabetes. Control 2 and control 3 group included patients with stage I gastric cancer and BMI&lt;25, with/without type 2 diabetes. Macrophage accumulation and polarization were evaluated from visceral fat, collected during surgery, through histology, flow cytometry, and RT-PCR. Diabetic and inflammatory indices were assessed preoperatively and postoperatively 12 months. Experimental group were additionally analyzed based on postoperative diabetic remission and preoperative ABCD score.</p> Results <p> Patients with obesity (experimental and control 1) exhibited higher macrophage accumulation (<i>p</i>&lt;0.001), M1 polarization (<i>p</i>&lt;0.001), insulin resistance, WBC, CRP, and M1 marker (PELI1) than patients without obesity. Experimental group showed significantly higher macrophage accumulation (<i>p</i>&lt;0.001). M1 dominance was observed in patients achieving complete remission postoperatively or with ABCD score≧7 preoperatively.</p> Conclusion <p> Patients with obesity and diabetes (experimental) demonstrated macrophage accumulation, M1 polarization, and proinflammatory circumstance. Preoperative M1 dominance with proinflammatory circumstances may be associated with better diabetic remission after bariatric surgery.</p>