Benign prostatic hyperplasia (BPH) and overactive bladder (OAB) are common conditions in adult men and women. The use of Epilobium angustifolium extract has garnered attention, especially in Europe. Clinical trials have revealed that E. angustifolium extract may improve symptoms of BPH and OAB. Additionally, this extract contains Oenothein B, an ellagitannin, and has been reported to have anti-inflammatory, antioxidant and anti-ageing effects. The mechanism of Oenothein B’s anti-inflammatory and antioxidant effects is unclear. Therefore, this study evaluated the autophagy activity of Oenothein B to determine if E. angustifolium extract containing Oenothein B activates autophagy. To evaluate the autophagy activity of E. angustifolium extract containing Oenothein B, we used the tfLC3 assay, which evaluates the formation of autolysosomes. E. angustifolium extract containing Oenothein B activates autophagy starting at 0.01 mg/mL. The results suggest that E. angustifolium extract containing Oenothein B activates autophagy, potentially exerting anti-inflammatory and antioxidant effects through this activation.