Background: Long course radiotherapy plus neoadjuvant chemotherapy followed by resection (total mesorectal excision, TME) has accepted widespread recognized in the treatment of locally advanced rectal cancer (LARC). Tislelizumab, an anti-PD1 humanized IgG4 monoclonal antibody, has been demonstrated with clinical activity and is approved for treating recurrent/refractory classical Hodgkin lymphoma and locally advanced/metastatic urothelial carcinoma in China. However, the safety and efficacy of long course (neoadjuvant chemoradiotherapy, NCRT) plus tislelizumab followed by TME for LARC is still uncertain. Methods: This NCRT-PD1-LARC trial will be a prospective, multicenter and phase II clinical trial designed to evaluate the safety and efficacy of LARC patients treated with long course NCRT plus tislelizumab followed by TME. This trial will consecutively enroll 50 stage II/III LARC patients (cT3N0M0 and cT1-3N1-2M0) with the tumor distal location <= 7 cm from anal verge at 7 centers in China. The enrolled patients will receive long course radiotherapy (50 Gy/25 f, 2 Gy/f, 5 days/week) and three 21-day cycles capecitabine (1000 mg/m(2), bid, po, day1-14) plus three 21-day cycles tislelizumab (200 mg, iv.gtt, day8), followed by TME 6-8 weeks after the end of radiotherapy. The primary efficacy endpoint will be the pathological complete response (pCR) rate, which is defined as absence of viable tumor cells in the primary tumor and lymph nodes. Discussion: To our knowledge, this trial is the first multicenter clinical trial in China to assess the safety and efficacy of NCRT plus anti-PD1 therapy followed by TME to treat patients with LARC. NCRT followed by TME was recognized as the most recommended treatment against LARC while could not be completely satisfied in clinic. This study expects to provide a solid basis and encouraging outcomes for this promising combination of radiotherapy, chemotherapy and immunotherapy in LARC.