Somatic mutations of DNMT3A gene have recently been reported in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). We examined the entire coding sequences of DNMT3A gene by high-resolution melting analysis and sequencing in Chinese patients with myeloid malignancies. R882 mutations were found in 12/182 AML and in 4/51 MDS, but not in either 79 chronic myeloid leukemia (CML), or 57 myeloproliferative neoplasms (MPNs), or 4 chronic monomyelocytic leukemia. No other DNMT3A mutations were detected in all patients. R882 mutations were associated with old age and more frequently present in monoblastic leukemia (M4 and M5, 7/52) compared to other subtypes (5/130). Furthermore, 14/16 (86.6%) R882 mutations were observed in patients with normal karyotypes. The overall survival of mutated MDS patients was shorter than those without mutation (median 9 and 25 months, respectively). We conclude that DNMT3A R882 mutations are recurrent molecular aberrations in AML and MDS, and may be an adverse prognostic event in MDS.