BACKGROUND: Despite the established oncological benefits of neoadjuvant chemotherapy for esophageal squamous cell cancer, not all cases demonstrate benefit. Hence, predicting the response to chemotherapy before treatment is desirable. Some reports have shown that immune factors are related to the chemotherapy response. This study aimed to investigate the utility of serum IgG levels for predicting chemotherapy response. METHODS: Among the patients who underwent esophagectomy after neoadjuvant chemotherapy at Nagoya City University Hospital between December 2012 and June 2019, 130 cases were included in this study. Response to chemotherapy and pretreatment serum IgG levels were examined in 77 cases. FP (5-fluorouracil and cisplatin) therapy or DCF (docetaxel, cisplatin, and 5-FU) therapy was performed as neoadjuvant chemotherapy. DCF therapy was selected for patients aged <75 years, who could be safely administered chemotherapy based on their medical history. RESULTS: This study divided cases into two groups: the effective response group (PR) and ineffective response group (SD and PD). We classified 1, 37, and 39 cases as PD, PR, and SD, respectively. None of the cases were classified as CR. The effective response group had significantly lower serum IgG levels than the ineffective response group (p < 0.001). The cutoff serum IgG value was determined to be 1087 mg/dL. The low IgG group had significantly more cases who had effective response to chemotherapy compared with the high IgG group (odds ratio [OR] = 9.009; 95% confidence interval [CI] = 2.974-30.157; p < 0.001). Univariate and multivariate analyses revealed serum IgG level to be an independent predictor for response to chemotherapy (p = 0.001). Furthermore, cases with effective pathological response had significantly lower pretreatment serum IgG levels than those who did not (p = 0.006). CONCLUSIONS: Our finding showed that serum IgG levels can be an independent predictor of the response to neoadjuvant chemotherapy for esophageal squamous cell carcinoma. TRIAL REGISTRATION: This retrospective study was approved by the review board of Nagoya City University Graduate School of Medical Sciences (reception number: 60-18-0008 ).