This prospective, single-center, single-arm, open-label clinical study aims to evaluate whether autologous fecal microbiota transplantation can improve bowel and anal function after ileostomy reversal in patients with rectal cancer who underwent radical rectal cancer surgery with protective loop ileostomy. Eligible patients will receive autologous fecal microbiota transplantation before ileostomy reversal. The primary outcome is the Low Anterior Resection Syndrome score at 3 months after ileostomy reversal. Secondary outcomes include fecal incontinence score, colonoscopic findings before ileostomy reversal, gut microbiota profiles, inflammatory markers, anorectal manometry, pelvic floor electromyography, and safety outcomes.