Background: Many studies proved high percentage of vitamin D deficiency in psoriatic arthritis patients. Different records about the possible link between vitamin D deficiency and state of inflammatory & disease activity in psoriatic arthritis patients). Aim of the work: To evaluate the vitamin D level in Egyptian patients with psoriatic arthritis and its association with activity of the disease as well as disease severity. Patients & Method: 45 Psoriatic Arthritis Patients fulfilled the Classification Criteria for the diagnosis of Psoriatic Arthritis (CASPAR) and 50 healthy controls were included. Medical history was taken, general and musculoskeletal examination were done. Disease activity was assessed using the Disease activity in psoriatic arthritis "DAPSA" score. VAS, HAQ, ESR & CRP were done. Serum level of 25(OH) vitamin D was measured by ELISA for patients and controls. Results: Serum vitamin D level in psoriatic arthritis patients ranged from 10-48 ng/mL, with mean ±SD 32.844±12.395. While in healthy controls it ranged from15-50 ng/mL with mean ±SD33.940±8.998, without statistical significant difference. Vitamin D deficiency was detected in 12 patients (26.6%) and 5 (10%) healthy participants with statistically significant higher frequency of vitamin D deficiency in patients than controls (P-value <0.034). patients with vitamin D deficiency showed statistically significant longer disease duration, higher VAS, HAQ score, ESR, CRP titer and DAPSA score (P-value <0.001). Also, they had statistically significant higher frequency of axial affection (P-value <0.001). Vitamin D level was statistically negatively correlated with disease duration, VAS, HAQ, ESR, CRP and DAPSA score (P-value <0.001). Conclusions: We concluded that psoriatic arthritis patients had higher frequency of vitamin D deficiency than healthy individuals. And that patients with vitamin D deficiency had more active and more severe disease compared to those without deficiency.