The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the production of antiphospholipid antibodies (aPL) that promote vascular thrombosis and pregnancy loss. APS can occur in the absence of underlying or associated disease (primary APS) or in combination with other diseases (secondary APS). Mean platelet volume (MPV) is largely regarded as a useful surrogate marker of platelet activation. We aimed to investigate if there is a relationship between MPV and thrombotic events in APS. The study consisted of 22 patients and 22 healthy controls. Group 1 is defined as all the patients in the first day of thrombotic event. Group 2 is defined as the same patient population three months after the thrombotic event. The erythrocyte sedimentation rate, C-reactive protein, white blood cell count, platelet count, and MPV levels were retrospectively recorded from patient files. Statistical analyses showed that MPV was significantly higher in group 1 than group 2 (p<0.0001) and healthy controls (p<0.05). However, there was no difference between group 2 and healthy controls (p=0.888). WBC, hemoglobin and other platelet indices such as platelet distribution width and platecrit did not differ in groups. In conclusion, MPV was increased at initial thrombotic event of APS, and then it was normalized three months later by therapeutic interventions. To our knowledge, this is the first study demonstrating a correlation between MPV and thrombotic events in APS.