Background: Systemic lupus erythematosus (SLE) is autoimmune disease needs continuous assessment of disease activity. There is no single biomarker used for that purpose. Platelet indices have recently been found to be a simple inflammatory marker used in the assessment of systemic inflammation in many diseases like, rheumatoid arthritis, ankylosing spondylitis and inflammatory bowel diseases. Aim of Study: To evaluate platelet indices [mean platelet volume (MPV), platelet distribution width (PDW) and plateletcrit (PCT)] as markers of disease activity in patients with SLE. Patients and Methods: In this cross sectional study we tested 100 subjects; 20 healthy control and 80 SLE patients recruited from rheumatology unit in Internal Medicine Department, Tanta University, Tanta, Egypt. Then the lupus patients were divided according to SLEDAI into 20 patients without flare (SELEDAI <4), 17 patients mild flare (SELEDAI 4-<8), 25 patients moderate flare (SELEDAI 8-<12) and 18 patients severe flare (SELEDAI >_ 12). Platelet indices (MPV, PDW, PTC) were assessed in all of them and their correlation to SLEDAI score were analyzed. Results: MPV and PDW had no clinical significance in assessing lupus activity, PCT significantly lower with SLE patients with severe flare and it had a significant negative correlation with SELEDAI score with cutoff value equals <_0.173, sensitivity 61.11%, specificity 79.03%, PPV 45.8% and NPV 87.5%. Finally there was no significant difference between lupus nephritis and lupus without nephritis patients in Platelet indices. Conclusion: Plateletcrit (PCT) can be used as a new marker for SLE activity.