Background: Previous research on mean platelet volume (MPV) in relation to disease activity in systemic lupus erythematosus (SLE) is sparse and conflicting. Although MPV is simple and inexpensive, few studies have investigated its role in patients with SLE and it remains unclear whether MPV is associated with SLE activity or not. Objectives: This study aimed to ascertain MPV levels in SLE patients with and without activity. Additionally, to determine the association between MPV and lupus activity. Patients and methods: 74 patients diagnosed with SLE and 74 healthy controls gender- and age-matched were registered in this research. Patients were split into two groups based on Systemic Lupus Erythematosus Disease Activity Score (SLE-DAS). Data concerning sociodemographic information and MPV were recorded in both patients and controls. Results: According to SLE-DAS, 41 patients with SLE were active, whereas 33 had inactive disease. Active SLE patients had diminished mean values of MPV compared to inactive disease group and control group (8.4 ± 0.7 fl versus 10.2 ±1.3 fl versus 10.9 ± 0.4 flrespectively, p=0.001). MPV correlated significantly to lupus activity determined by SLE-DAS (r=0.44, p=0.01). Conclusions: MPV levels were significantly diminished in SLE patients than in healthy controls, and they were much diminished in active disease than in inactive group. MPV was correlated significantly with lupus activity. MPV can be used as a simple, available and low-cost laboratory assessment for evaluation of disease activity in SLE patients.