Mycosis fungoides (MF) is the most common form of cutaneous T-cell lymphoma. Histopathologically, MF can show superficial atypical lymphoid infiltration with epidermotropism. We report a case of MF patient who showed atypical histological findings. A 76-year-old male presented with multiple various sized erythematous patches with peripheral rim on the trunk. 2 years ago, he had been treated with excimer laser under diagnosis of granuloma annulare, without improvement. Physical exam revealed multiple erythematous plaques with peripheral rim limited on the trunk. We performed skin biopsy. Histopathological findings showed perivascular atypical lymphocytes infiltration without epidermotropism. A large number of dermal lymphocytes showed positive reactivity for CD4 in immunophenotyping. T cell receptor (TCR) gene rearrangement study showed monoclonality. He was finally diagnosed MF by confirming the monoclonality of the TCR gene rearrangement. He was treated with MTX and NBUVB therapy for 3 months. The patient remained in good condition for 6 months without recurrence. Early MF is difficult to diagnose, and in the absence of an accurate diagnosis, patients often show resistant to any treatment. We suggest that atypical histopathologic findings were caused by the patient's past excimer laser treatment. Here, we report MF with atypical histopathologic findings which successfully treated with MTX and phototherapy.