Background: Chronic endometritis (CE) significantly contributes to repeated implantation failure (RIF). Although antibiotics are common treatments for CE, some patients do not achieve resolution. Therefore, the use of an alternative method involving the administration of ImmuBalanceTM (IMB), a combination of pre- and probiotics, was explored in the current study. Methods: This retrospective study was conducted between April 2021 and August 2022. A total of 819 women with CE were treated with antibiotics-1 (doxycycline, n=809) or IMB (n=10, Group 1). Following endometrial biopsies, CE was not resolved in 209 out of 819 women. Subsequently, 194 patients were treated with antibiotics-1 (n=4) or -2 (amoxicillin, azithromycin, and metronidazole, n=190), whereas 15 were treated with IMB (n=15, Group 2). After the treatment with antibiotics-2, four women underwent IMB (Group 3). Statistical analysis of the number of plasma cells with CD138 before and after treatment was conducted using Fisher’s exact test and p-values <0.05 were considered statistically significant. Results: CE was treated in 60% of patients (6/10) in Group 1; however, the reduction in CD138 count was not statistically significant (p=0.13). In Groups 2 and 3, CE was treated with a significantly reduced CD138 count (Group 2, p<0.01; Group 3, p=0.04). CE was treated in 100% of cases in Group 2 and 3 (15/15 and 4/4, respectively). Conclusion: Based on the findings of this study, administration of IMB may be effective in treating CE, especially following antibiotic treatment.