Background: Red blood cell distribution width (RDW) and mean platelet volume (MPV) are influenced by autoimmune diseases as RA. Objective: This study aimed to assess RDW, MPV levels and different hematological indices in ankylosing spondylitis (AS) and psoriatic arthritis (PsA) to investigate their relations with disease activity. Methods: A total of 120 patients (60 AS and 60 PsA) were enrolled. Demographic data, disease activity scores, complete blood count (CBC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were recorded. RDW, MPV and various ratios were measured. Results: Patients mean age was 44.750 ± 12.187S years were elevated in PsA and AS patients. RDW and MPV were significantly higher in patients with active PsA patients (14.495 ± 1.9 and 8.903 ± 1.166fl) than in inactive ones (11.975 ± 0.5fl and 8.220 ± 0.5 fl, p value <0.001, 0.014 respectively). While in AS active patients RDW was elevated in patients with high bath ankylosing Spondylitis disease activity index (BASDAI) score. RDW% was positively correlated to disease activity among PsA and AS patients (r=0.614 p <0.001) and (r=0.567 p <0.001) respectively. In AS patients, RDW was at a criterion of 12.4, with sensitivity of 83.78% and specificity of 69.5% (p value < 0.001), while in PsA patients' RDW showed good metrics [p value < 0.001; Cutoff:13.2; sensitivity: 72.5%; specificity: 100%]. Conclusion: RDW and MPV were potentially elevated in active psoriatic patients and RDW were positively correlated with activity score of AS and PsA, which could be possible important index for disease activity.