Objective  To explore the correlation between red cell distribution width (RDW) and prognosis of idiopathic interstitial pneumonias (IIPs). Methods  A total of 61 patients with confirmed diagnosis of IIPs were divided into the survival group and death group by using death/survival as end point of observation. Their clinical data were recorded. The risk factors of IIPs were analyzed and the correlation between RDW and prognosis of IIPs was explored. Results  Among 61 patients, 33 were males and 28 were females, the ratio of male and female was 1.2∶1, and the average age was 64.60±16.33. Compared with the survival group (n=26), the average age of death group (n=35) was higher (P=0.004) and respiratory failure was severer (P=0.002). The baseline value of RDW of all patients was (15.12±1.71)% and last value of RDW was (16.30±2.54)%. The baseline value and last value of RDW of the death group were (15.95 ± 1.50)% and (17.84±2.26)% and significantly higher than those of the survival group (P=0.000).  Logistic multivariate analysis showed that RDW was an independent factor for predicting the prognosis of IIPs based on gender and age being controlled. The threshold value for predicting the prognosis of IIPs by RDW was 15.70% and the area under receiver operating characteristic (ROC) curve was 0.94 (95%CI: 1.61-1.95) with the sensitivity of 88.60% and specificity of 96.20%. The mortality of patients with RDW≥ 15.70% was significantly higher than that of patients with RDW<15.70% (P=0.000). Conclusion  RDW independently correlates with severity of IIPs and is an independent factor for predicting the prognosis of IIPs.