Treatment with ribonuclease (RNase) reportedly protects the heart after myocardial ischemia–reperfusion (I/R), but its potential effect on lung I/R injury (LIRI) is unknown. Thus, we aim to explore whether RNase treatment would relieve LIRI. Thirty-six C57BL/6J adult male wild-type mice were evenly divided into I/R + RNase (I/R + R) group, I/R group, and sham group. Lung I/R was induced by left pulmonary hilum occlusion for 1 h and reperfusion for 2 h. All mice were treated with RNase or same dosage of normal saline in advance. After I/R, blood and lung tissues were collected for analysis. The results showed that lung injury scores, wet/dry ratio, expressions of inflammatory cytokines, pulmonary apoptosis, and levels of serum extracellular RNA (exRNA), including microRNAs, were markedly elevated after I/R. However, RNase treatment significantly attenuated cytokine production in both lung tissue and serum and also suppressed pulmonary apoptosis as reflected by TUNEL staining and activated caspase-3. In addition, total serum exRNA levels in the I/R + R group had a downward trend versus the I/R group. In conclusion, the increase of circulating exRNA levels contributed to LIRI in adult mice, which could be relieved by injection of RNase during perioperative window. The potential mechanism is the decrease of serum exRNA level and the suppression of pulmonary inflammation and apoptosis.