Objective To determine the value of mean platelet volume (MPV) and platelet large cell ratio (P-LCR) in the diagnosis of acute coronary syndrome (ACS) in patients with chest pain. Methods A total of 83 chest pain patients with identified ACS and 56 chest pain patients without cardiovascular disease in our hospital from January to June 2013 were subjected in this study. Their venous blood samples were collected within 6 h of onset for platelet parameters. Mean comparison between the 2 groups and logistic regression analysis were used to find the effective platelet parameters, and receiver operating characteristic (ROC) curve analysis was used to evaluate their diagnostic significances for ACS. Results ACS group had significantly lower platelet than the non-cardiac chest pain group [(191.28±67.07)×109 vs (236.75±64.09)×109/L)], and significantly higher MPV [(11.88±1.24) vs (10.73±1.08)fL], platelet distribution width (PDW) [(15.54±1.87) vs (13.40±2.35)fL] and P-LCR [(47.49±9.55)% vs (35.11±10.00)%] (all P＜0.05). There was no statistical difference in the platelet parameters among different types of ACS patients (P＞0.05). Logistic regression analysis showed that P-LCR and MPV were auxiliary diagnostic indicatos for ACS. ROC curve analysis showed that the cut-off was 0.15μg/L, 38.5%, 11.05fL, and 19.0U/L, respectively, for troponin I (TnI), P-LCR, MPV and creatine kinase-MB (CK-MB), and their areas under the curve were 0.987, 0.817, 0.754 and 0.598, respectively. Their sensitivity was 97.3%, 92.8%, 71.1% and 45.8% respectively, the specificity were 90.3%, 64.3% 62.5%, and 73.2% respectively, and the diagnostic accuracy were 100%, 80%, 72.6%, and 67.2%, respectively for TnI, P-LCR, MPV and CK-MB. Conclusion MPV and P-LCR are helpful in the early diagnosis of ACS, and can be seperately used as auxiliary diagnostic indicators of ACS in patients with chest pain. Because of their high diagnostic accuracy, the 2 parameters can be served as a reference for early prediction and differential diagnosis of ACS.