With expansion of the COVID-19 pandemic, reports of post-COVID-19 interstitial lung disease (ILD) have been emerging. However, there are few reports regarding treatment. Some reports indicate that corticosteroids are effective for post-COVID-19 ILD, but the use of long-term corticosteroid carries risks of side effects. We administered tacrolimus to an elderly patient with post-COVID-19 ILD who suffered a respiratory failure relapse during steroid tapering. The respiratory status improved with tacrolimus in the post-acute phase, but pulmonary fibrosis progressed in the late phase. Tacrolimus may be effective for treating post-COVID-19 ILD in the post-acute phase, but it does not halt progression of pulmonary fibrosis.