Systemic lupus erythematosus (SLE) is a disease of the immune system with an unknown etiology. It is a unique disease that has a wide range of clinical and laboratory findings according to the organ or system involved and the activity of the disease. Mean platelet volume (MPV) is a simple parameter of the blood and is widely and easily available. It has been evaluated as a sign of inflammation in many kinds of diseases recently. In this study, we retrospectively analyzed the laboratory parameters and clinical features of 36 SLE patients with renal involvement and nephrotic-range proteinuria in the active and remission periods of the disease between 2005 and 2013. We found that the mean MPV in the active disease of the period was statistically significantly higher than in the remission period (8.30 ± 1.09 and 7.88 ± 0.7, respectively, P = 0.007).