Objective:To explore the genetic characteristics, clinical features, and prognostic values of RAS mutations in patients with myelofibrosis (MF) .Methods:We analyzed 112-gene targeted sequencing data from 226 patients who had a diagnosis of either primary myelofibrosis (PMF) or post-polycythemia vera/post-essential thrombocythemia (post-PV MF and post-ET MF) from December 2011 to December 2019. A retrospective analysis of the genetic characteristics, clinical features, and prognosis of RAS mutations was performed.Results:Among 266 patients diagnosed PMF or post-PV/ET MF, RAS mutations were found in 14 (6.2%) cases, including 9 (4.0%) cases of NRAS mutations, 8 (3.5%) cases of KRAS mutations, and 3 (1.3%) cases of both NRAS and KRAS mutations. All of the NRAS mutations were located in codons 12 and 13. The median VAFs of RAS mutations were significantly lower than those of the driver mutations, confirming that they represent sub-clonal events that are acquired during the disease course. SETBP1, SRSF2, and MPL tended to be clustered with RAS mutations. Patients with RAS mutations had a higher number of additional oncogenic mutations (median, 3.36 vs 1.17, P<0.001) . RAS mutations had a statistically significant association with elevated monocyte cell counts ( P=0.003) , lower platelet counts ( P=0.026) , higher bone marrow blasts ( P=0.022) , splenomegaly ( P=0.005) , and very high-risk (VHR) karyotype abnormality percentage ( P=0.031) . In univariate analysis, the OS of patients with NRAS mutations were significantly inferior in the entire MF and PMF cohorts ( P=0.001, P=0.008) . In a multivariate model, NRAS retained an independent negative prognostic factor in PMF. Conclusion:RAS gene mutations were constantly related to elevated monocyte cell counts, lower platelet counts, higher bone marrow blasts, and VHR karyotype abnormality percentage that usually defined high-risk disease and often occurred as sub-clonal events. NRAS mutation is an independent poor prognostic factor in PMF.