Aims Corticosteroids are widely used in patients with cardiac sarcoidosis (CS). In addition, upgrading to cardiac resynchronization therapy (CRT) is sometimes needed. This study aimed to investigate the impact of corticosteroid use on the clinical outcomes following CRT upgrades. Methods A total of 48 consecutive patients with non-ischemic cardiomyopathies who underwent CRT upgrades were retrospectively reviewed and divided into three groups: group 1 included CS patients taking corticosteroids before the CRT upgrade (n = 7), group 2, CS patients not taking corticosteroids before the CRT upgrade (n = 10), and group 3, non-CS patients (n = 31). The echocardiographic response, heart failure hospitalizations, and cardiovascular deaths were evaluated. Results The baseline characteristics during CRT upgrades exhibited no significant differences in the echocardiographic data between the three groups. After the CRT upgrade, responses regarding the ejection fraction (EF) and end-systolic volume (ESV) were significantly lower in CS patients than non-CS patients (ΔEF: group 1, 6.7% vs. group 2, 7.7% vs. group 3, 13.6%; p=0.039, ΔESV: 3.0 mL vs. -12.7 mL vs. -37.2 mL; p = 0.008). The rate of an echocardiographic response was lowest in group 1 (29%). There were, however, no significant differences in the cumulative freedom from a composite outcome among the three groups (p = 0.19). No cardiovascular deaths occurred in group 1. Conclusion CS patients taking corticosteroids before the CRT upgrade had lower echocardiographic responses but higher freedom rates from a composite endpoint. The timing of corticosteroid use would affect the clinical course following a CRT upgrade.