Psoriasis is a chronic, recurrent, and immune-mediated inflammatory disease that affects 2–3% of the world population. The present study aimed to evaluate serum folate level before and after oral PUVA therapy in psoriatic patients. Patient and methods: A total of 40 psoriatic patients without any other morbidities (age ranged from 19 to 63 years, including 20 males and 20 females), All the patients recieved oral 8-methoxypsoralen at a dose of 0.6 mg/kg, followed 2 hours later by ultraviolet A exposure (oral PUVA therapy), For each patient the therapy will be twice weekly for eight weeks. Patients in the PUVA group were treated twice times weekly with a starting dose of 2 J/cm², increasing by 20% each session, to a maximum of 15 J/cm² per dose. Patients underwent up to 16 sessions. The dosage was adjusted if patients developed erythema. We have measured serum folate levels at baseline and after oral PUVA exposure. Also we use PASI score as objective method to visualize the relationship between improvement of psoriasis and changes in folate serum levels at baseline and after 16 exposures to PUVA for 8 weeks along with subjective methods which were done by photography and adverse effects were also reported. Results: There is statistically significant decrease of folic acid level after 16 sessions of phototherapy by average 20%. According to PASI score, Our results shows that there is statistically significant improvement in PASI score after phototherapy by average 60% .Conclusion: Folate deficiency should be evaluated and corrected in the patients, as it may be aggravated by UV therapy.