Background: 70% of esophageal carcinoma are unresectable at diagnosis. Despite active clinical research on the treatment of esophageal squamous cell carcinoma (ESCC), the long-term survival rate of advanced patients is still very low, with a 5-year survival rate of 30%-40%. A prospective, randomized-controlled, double-blinded, multicenter, and phase III study (NXCEL1311) was designed to investigate the efficacy and safety of nimotuzumab (anti-EGFR humanized monoclonal antibody;abbreviate,Nimo) plus concurrent chemo-radiotherapy compared with placebo plus chemo-radiotherapy in unresectable locally advanced ESCC. Methods: Unresectable locally advanced ESCC patients were randomized (1:1) to receive Nimo (400 mg, qw) or placebo in combination with concurrent chemo-radiotherapy (paclitaxel+ cisplatin+3DCRT/IMRT) for seven weeks. Patients were followed for five years.The primary endpoints were OS, and the secondary endpoints included ORR, DCR, PFS. Results: 200 patients were assigned to the Nimo group (n = 99) or placebo group (n = 101). An interim analysis was conducted for short term efficacy, i.e secondary endpoints (ORR, DCR) and safety, after completing the 6 months follow-up. The OS events are not enough for analysis. The two groups were comparable on baseline characteristics. Eighty patients in the Nimo group and eighty-two patients in the placebo group were evaluable. The ORR of the Nimo group (75/80, 93.8%) was significantly higher than the placebo group (59/82, 72.0%;Chi-square test, p < 0.001). Twenty-six patients in the Nimo group reached the complete response (CR), and ten placebo group patients were CR. The CR rate in the Nimo group was significantly higher than placebo group (32.5% vs.12.2%, p = 0.002). The DCR of the Nimo group and placebo group were 98.8% (79/80) and 91.5% (75/82), respectively (p = 0.064). Single factor logistic aggression analysis showed that age, sex, target lesion number, and BMI did not affect ORR, CR, and DCR (p > 0.05). Multiple factor correction analysis showed the difference of CR, ORR and DCR between two groups is 20% (95%CI 6.0%̃40.2%), 30% (95%CI 10.6%̃52.1%) and 10% (95%CI -5.2%̃31.1%). The incidence of grade 3-5 drug-related AEs was 11.1%vs.10.9% (p > 0.05). Common drug-related AEs in patients with Nimo plus chemo-radiotherapy treatment were leucopenia, neutrophilic granulocytopenia, thrombocytopenia, hemoglobin, bone marrow inhibition, nutritional anemia, and radioactive inflammation. Conclusions: This interim analysis showed that nimotuzumab in combination with chemo-radiotherapy is safe and can increase the CRR and ORR of the treated patients. The OS needs to be followed and finally analyzed. Clinical trial information: 02409186.