Objective To explore the effects of fat-free mass index FFMI on postoperative complications and in-hospital mortality and clarify its predictive value for perioperative outcomes of esophageal cancer patients. Method This analysis included 152 esophageal cancer patients who underwent curative esophagectomy at the Department of Thoracic Surgery in Haian Hospital Affiliated to Nantong University from January 2017 to December 2021. The FFMI was measured and calculated by bioelectrical impedance analysis and then all patients were divided into low FFMI 103 and normal FFMI 49 group based on the cutoff value of FFMI male <17 kg / m 2 female < 15 kg / m 2 . The baseline characteristics and perioperative outcomes of the two groups were compared. In addition the Logistic regression model was used for univariate and multivariate analysis to determine the independent risk factors of postoperative complications for esophageal cancer patients. Result Except for body mass index there were no significant differences between low FFMI and normal FFMI group for age gender comorbidities clinicopathological features and laboratory tests P>0. 05 . The baseline characteristics between the two patient groups were comparable. Compared with the normal FFMI group low FFMI group had a higher rate of postoperative complications 40. 8% vs 21. 4% χ 2 = 6. 286 P = 0. 012 especially anastomotic leakage 40. 8% vs 21. 4% χ 2 = 5. 191 P= 0. 032 and pneumonia 28. 6% vs 12. 6% χ 2 = 5. 783 P = 0. 016 . In addition the length of hospital stays was longer in low FFMI group than in the normal FFMI group IQR 14. 0 12. 0 18. 0 d vs 12. 0 11. 0 16. 0 d Z = - 1. 985 P = 0. 047 . However there was no significant difference between the two groups for postoperative in-hospital mortality 4. 1% vs 1. 9% χ 2 = 0. 593 P= 0. 388 . The results of univariate and multivariate logistic regression analysis revealed that preoperative FFMI OR = 2. 502 95%CI = 1. 181 - 5. 301 P = 0. 017 and hypoalbuminemia OR = 2. 570 95% CI = 1. 115 - 5. 926 P = 0. 027 were independent risk factors of postoperative complications for esophageal cancer patients who underwent curative esophagectomy. Conclusion FFMI was an effective parameter to predict the perioperative outcome and this finding further emphasized the value of body composition measurement in the clinical management of esophageal cancer patients.