Mesenchymal stem cells (MSCs) are a type of multipotent, non-hematopoietic cells of mesodermal origin. Due to their strong immunomodulatory, immunosuppressive, and regenerative potential, MSCs are used in cell therapy for inflammatory, immune-mediated, and degenerative diseases. Exosomes derived from MSCs have several advantages over MSC therapy, including non-immunogenicity, lack of infusion toxicity, ease of isolation, manipulation, and storage, cargo specificity, and the absence of tumor-forming potential and ethical concerns. We hypothesized that preconditioning human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) with the proinflammatory cytokines interleukin 17 (IL-17), IL-22, and tumor necrosis factor alpha (TNF-α), the increased levels of which are typical in psoriasis patients, can significantly increase the therapeutic efficacy of both hUCB-MSCs and their exosomes (hUCB-MSC-Exo). Our aim was to compare the therapeutic effects of hUCB-MSCs preconditioned with various combinations of proinflammatory cytokines and their hUCB-MSC-Exo, in an in vivo imiquimod-induced psoriasis-like skin inflammation model in mice. Our results showed a significant attenuation of psoriasis symptoms (erythema, scaling, and skin thickness) in mice treated with intact hUCB-MSCs, hUCB-MSCs preconditioned with IL-22 and TNF-α, and hUCB-MSC-Exo preconditioned with IL-17, IL-22 and TNF-α (MSC-Exo 3C). However, the most pronounced therapeutic effect was observed with MSC-Exo 3C treatment. In summary, we demonstrated that MSC-Exo 3C transplantation has therapeutic potential for treating psoriasis-like skin lesions.