Background/Objectives: Ultrasonography (US) is a non-invasive and repeatable examination for evaluating chronic constipation. However, only few studies have investigated drug therapy decisions based on rectal US results. To date, the efficacy and safety of elobixibat have not been evaluated using rectal US classification in patients with chronic constipation. This study aimed to evaluate the efficacy and safety of elobixibat in patients with chronic constipation classified as “no fecal retention” by rectal US. Methods: We retrospectively analyzed 32 patients with chronic constipation who underwent rectal US and received elobixibat (10 mg/day) between May 2019 and December 2024. Patients were classified into four groups according to rectal US findings: no fecal retention, fecal retention without hard stools, fecal retention with hard stools, and gas retention . The primary endpoint was the respon se rate of spontaneous bowel movements (SBMs) within 3 days after starting elobixibat in the “no fecal retention” group. Results: Among 18 patients in the “no fecal retention” group, 94.4% achieved SBMs within 3 days after elobixibat administration, indicating a favorable response. Adverse events included abdominal distension and abdominal pain, each observed in one patient (3.1%). Conclusions: Elobixibat was effective and well tolerated in patients with chronic constipation classified by rectal US findings.