Background Psoriatic arthritis (PsA) is an inflammatory disorder affecting the joints of psoriatic patients. Gelsolin regulated the actin assembly and disassembly. Reduction in plasma gelsolin levels was detected in tissue damages, including trauma, sepsis, and chronic inflammatory disorders. Objectives The study aims to investigate the potential role of gelsolin in PsA and to determine the association between gelsolin and the disease activity. Methods Plasma gelsolin levels were measured in 76 PsA patients in comparison with 40 patients having psoriasis only and 40 age- and sex -matched healthy controls. Results Plasma gelsolin levels were decreased in PsA patients compared to controls and psoriasis-only patients (p ˂ 0.0001). The optimal cutoff point of gelsolin was 172.5 mg/L. Gelsolin showed 92.1% sensitivity and 95% specificity in detecting PsA. But, it had 92.1% sensitivity and 80% specificity in differentiating between psoriasis and PsA. Plasma gelsolin showed a significant negative correlation with inflammatory markers as C-reactive protein and erythrocyte sedimentation rate (p < 0.0001 and p = 0.039; respectively). A significant negative correlation between plasma gelsolin and PsA activity was detected (p < 0.0001). The PsA activity was defined by the Disease Activity for Psoriatic Arthritis Score and the Composite Psoriatic Disease Activity Index. Conclusions The plasma gelsolin levels were decreased in PsA patients, suggesting that gelsolin may be implicated in the chronic joint inflammation process. Plasma gelsolin seems to be a useful predictive biomarker for diagnosing PsA and monitoring the disease activity.