As small bowel adenocarcinoma (SBA) is a rare cancer worldwide, prognostic factors have not been clearly defined. The purpose of this study is to assess the prognostic role of clinicopathologic features, including body mass index (BMI), in patients with advanced SBA. A total of 28 consecutive patients with advanced SBA treated with palliative chemotherapy were retrospectively enrolled and analyzed. Clinicopathologic features, progression-free survival (PFS), and overall survival (OS) were compared according to BMI level. Eighteen patients had BMI < 25 kg/m(2) (overweight/normal/underweight in Asian) and ten patients had BMI ≥ 25 kg/m(2) (obese in Asian). Baseline characteristics were similar regardless of patient's BMI. Compared to patients with BMI < 25 kg/m(2), patients with BMI ≥ 25 kg/m(2) had higher response rate to chemotherapy (40.0% vs. 0%, P = 0.010), longer OS (11.2 vs. 7.0 months, P = 0.018) and a tendency toward prolonged PFS (2.1 vs. 1.9 months, P = 0.085). Multivariate analysis revealed that BMI ≥ 25 kg/m(2) is an independent positive prognostic factor of OS (adjusted hazard ratio 0.35, P = 0.024). In conclusion, baseline BMI ≥ 25 kg/m(2) has a positive prognostic role in patients with advanced SBA.