Background and Design: Methotrexate (MTX), a folic acid (folate) analog, is used for treatment of severe psoriasis or psoriatic arthritis. It has been reported that the homocysteine (Hcy) and folate levels were affected by low dose MTX treatment. In this study we investigated the effect of low dose MTX treatment on folate, vitamin B12 and plasma Hcy levels of patients with psoriasis vulgaris at early phase.,Material and Method: Sixteen patients (10 males, 6 females) diagnosed as moderate and severe psoriasis vulgaris and age-sex matched twenty healthy subjects (12 males, 8 females) were included in the study. Blood samples were drawn from the both groups before initiation of MTX treatment for folate, vitamin B12 and plasma Hcy measurements. Again, after 48 hours following 20 mg intramuscular MTX injection, blood samples of patients were drawn for folate, vitamin B12 and plasma Hcy level measurements,Results: While there were no significant differences in the folate and plasma Hcy levels between patients and healthy subjects (p>0.05), vitamin B12 levels were significantly lower in the patients than the controls (p<0.001). Although the decrease of folate and the increase of Hcy levels were significant compared to the initiation time of the treatment, there were no differences between the weeks. There was negative correlation between folate and Hcy levels before MTX treatment (rho:-0,54, p>0.05). There was no correlation been folate and Hcy levels after MTX treatment (p>0.05). Negative correlation was found between vitamin B12 and Hcy levels before and after treatment (p<0.05).,Conclusion: We concluded that low dose MTX treatment cause transient decrease of serum folate levels and transient increase of plasma Hcy levels that did not increase throughout the MTX treatment.