Background: Erythrocytes and platelets have been demonstrated to play a critical role in inflammatory processes. However, little is known about the diagnostic value of these indices in RA patients. The aim of this study was to evaluate the clinical significance of blood counts-related parameters such as counts of red blood cells (RBCs) and platelets (PLTs), hemoglobin (Hb), red blood cells-platelet ratio (RPR) and hemoglobin-platelet ratio (HPR) in rheumatoid arthritis (RA) and their association with disease activity. Methods: Clinical and laboratory data from 178 RA patients and 164 healthy controls were collected and analyzed. RA patients were divided into inactive group and active group according to disease activity score in 28 joints based on C-reactive protein (DAS28-CRP). The relationship between blood RBC, Hb, PLT, RPR and HPR and DAS28-CRP was detected by Spearman correlation method. Receiver operating characteristic (ROC) curve was used to assess the diagnostic value of these parameters. The predictive role of these indices for RA disease activity was evaluated by logistical regression analysis. Results: Active RA patients exhibited lower levels of blood RBC counts, Hb, HCT, RPR and HPR but significantly higher level of PLT counts compared with those in inactive groups (P < 0.01). Spearman analysis showed that blood RBC counts, HCT, RPR and HPR were negatively but PLT counts were positively related with DAS28-CRP (P < 0.001) in RA. ROC curve analysis revealed that the AUC of RBC and Hb was higher than that of ESR, RF and CCP for distinguishing active RA from inactive group. Logistical regression analyses showed that PLT is an independent predictor for RA disease activity. Conclusion: Blood RBC counts, Hb, RPR and HPR were negatively but PLT counts were positively related with RA disease activity. Blood PLT may act as a novel inﬂammatory factor for predicting disease activity in RA.