A 55-year-old female presented with widespread erythematous plaques with pustules on the whole body. According to her history, she had pruritic, multiple, erythematous eruptions of the whole body of 2-month duration and was treated with topical steroids and tacrolimus in other local clinic. Potassium hydroxide preparation revealed dermatophytic hyphae and the histopathologic examination also revealed multiple hyphae and spores on the stratum corneum. The fungus was identified as Trichoderma specise by fungus culture. She was diagnosed with tinea incognito. A significant improvement was observed after 2 weeks of topical antifungal agents and oral itraconazole 200mg/day. Tinea incognito is a dermatophytosis with atypical clinical presentation due to improper use of topical corticosteroids. Our case was characterized by pustular inflammatory skin lesions that could be mistaken for pustular psoriasis. Applying topical steroids masked the classical appearance of tinea and might accelerate the spread of dermatophytic infection. Tinea infection should be considered as a differential diagnosis of pustular dermatoses that are unresponseive to conventional treatment.