An 84-year-old thin, i.e., body mass index of 17.8, woman with gastric cancer underwent laparoscopic distal gastrectomy and lymph node dissection followed by Roux-en-Y reconstruction. During the operation, Nathanson liver retractor (NLR) was used to press the left lobe of the liver. The patient recovered uneventfully and was discharged on the 9th postoperative day. The patient, however, developed abdominal pain just on the day of discharge. Sudden onset of the abdominal pain and massive free air on computed tomography made us do diagnostic laparoscopy. Detailed laparoscopic observation showed slight liver swelling at the pressure site of the NLR, superficial band-shaped color change on the left lobe of the liver, and no anastomotic leakage, suggesting the massive free air caused by prolonged retention of postoperative intra-abdominal air. Two days later, persistent fever, inflammatory findings, and presumed liver abscess showing no healing tendency made us do ultrasound-guided aspiration to the liver focus. Bacterial culture test showed the bacterium <i>Escherichia coli</i>, being sensitive to meropenem. Despite the failure of abscess drainage, antibiotic therapy using meropenem gradually alleviated her symptoms and the patient was discharged from the hospital in 15 days after the abscess aspiration. Surgeons should note possible prolonged postoperative intra-abdominal free air and liver abscess without anastomotic leakage after laparoscopic gastrectomy especially in thin patients to avoid inappropriate postoperative management.