Objective To explore the molecular mechanism of pathogenesis and signal pathway of platelet activation in acute respiratory distress syndrome (ARDS). Methods Thirty healthy Sprague-Dawley rats were randomly divided into 5 groups. Four groups were intravenously injected with oleic acid (OA, 0.25 ml/kg) to establish ARDS rat model. One group was intravenously injected with normal saline (NS) in same dose as control group. After injection of oleic acid for 2 h, 6 h, 24 h, 72 h in four OA groups, and injection of saline for 2 h in the control group, the rats were sacrificed. Blood was sampled from the abdominal aorta, then platelets were separated for abstracting platelet protein. The mitogen-activated protein kinase kinase 3 (MKK3) phosphorylation level in platelet was detected by Western blot method, to explore the changes of platelet mitogen activated protein kinase (MAPKs) signal transduction pathway in ARDS, and the relationship between the changes and the pathogenesis of ARDS. Results Platelet MKK3 phosphorylation level significantly increased 6-72 h after injection of oleic acid (P＜0.05). It was 2.4 times that of the control group in 6 h group (0.50±0.09vs. 0.21±0.05), peaked and 3.7 times that of the control group in 24 h group (0.78±0.06), then fell slightly but still significantly higher than the control group in 72 h group (0.75±0.13). Conclusion The activation process of platelets is related with MKK3-p38 MAPK signaling pathway in ARDS.