Mycosis fungoides (MF) is the most common variant of cutaneous T-cell lymphoma (CTCL), which has T-helper type-2 (Th2)-dominant tumor microenvironment as its immunological milieu. Itching can be a distressing or even debilitating symptom in CTCL patients. However, the itching of MF is not relieved by conventional therapy using anti-histamines, which suggests that histamine is not the main pruritogen. Thus, the underlying mechanisms of itching in MF patients remain unclear. To determine the underlying mechanism of itching in MF, we investigated the clinical and histopathological features of MF patients. Thirty patients with MF who visited our hospital were investigated. Sixty percent of these patients reported itching (moderate itching: 40%, strong itching: 20%). The number of eosinophils infiltrating the skin was increased in the group with strong itching. IL-31 is a Th2 cytokine recently focused as a pruritogen. Although IL-31 is suggested to play a role in the itching of MF, the IL-31-immunoreactivity of the skin of the patients with itching did not differ from that of the patients without itching. On the other hand, both the kallikrein 5 (KLK5)-immunoreactivity and the serine protease activity of the patients’ skin were increased depending on the degree of itching. Taken together, these results suggest that KLK5 and eosinophil infiltration may be involved in the itching of patients with MF.