Mycosis fungoides is the commonest type of cutaneous T-Cell lymphoma. Janus kinases are intracellular tyrosine kinases that have recently been proven to have a crucial role in the pathogenesis and progression of several dermatological and malignant diseases.The aim of this study was to investigate the immunohistochemical expression of Janus Kinase-1 (JAK1) and Janus Kinase-3 (JAK3) in the skin of mycosis fungoides .The current study included 46 patients with early-stage MF, and 7 patients with late-stage MF, and 53 control samples. Immunohistochemical staining using JAK1 and JAK3 monoclonal antibodies was done in the skin specimens obtained from patients and controls. The evaluation of JAK1 and JAK3 gene expression using RT-PCR will be included in part 2 of the study.JAK1 immunohistochemical expression was nuclear, and JAK3 was cytoplasmic in MF patients. Immunoreactivity scores for JAK1 and JAK3 in MF patients were significantly increased compared to healthy controls (p < 0.001 and < 0.001, respectively). JAK1 and JAK3 immunoreactivity scores were significantly higher in the tumor than in the patch and plaque stages of MF (P7 = 0.001 and 0.004, respectively).This study is limited by the relatively small sample size of some clinical variants of mycosis fungoides, particularly advanced forms such as erythrodermic and tumor-stage MF. Further studies are needed to evaluate JAK1 and JAK3 expression following therapeutic interventions, including phototherapy and JAK inhibitors.JAK1 and JAK3 were significantly expressed in MF skin lesions in comparison to normal controls. JAK1 and JAK3 were more expressed in the tumor stage than patch and plaque stage MF, suggesting that JAK1 and JAK3 could play a crucial role in MF pathogenesis, progression, and prognosis.