Purpose: To report the clinical characteristics and treatment outcome of dematiaceous fungal keratitis initially misdiagnosed as a corneal foreign body.Case summary: A 51-year-old woman with a history of corneal opacity and recurrent ocular irritation presented with aggravated pain and a brown lesion in the right eye. A well-demarcated, elevated brown lesion located at the central cornea, corneal infiltration and epithelial defects were observed by slit-lamp examination. Anterior segment optical coherence tomography demonstrated posterior signal attenuation behind the brown lesion, with intact anterior chamber. Following removal of the lesion, fungal culture and potassium hydroxide (KOH) smear examination were performed. Yeast-like organisms exhibiting both hyphal and pseudohyphal forms were observed on KOH smear. For accurate identification of the fungus, molecular analysis using DNA sequencing was performed, confirming Cladophialophora boppii. After treatment with topical amphotericin B and oral itraconazole, corneal infiltration and clinical symptoms gradually improved. No recurrence was observed after discontinuation of antifungal therapy. Conclusions The patient presenting with a brown corneal lesion initially misdiagnosed as a corneal foreign body was diagnosed with dematiaceous fungal keratitis through microbiological culture and was successfully treated with antifungal agents.