The aim of this study was to evaluate the nucleophosmin (NPM1) gene exon 12 mutation in patients with acute myelogenous leukemia (AML) and its clinical characteristics. Genomic DNAs from 33 AML patients were amplified by PCR and sequencing for NPM1 mutations. The results showed that the NPM1 exon 12 mutations were found is 8 patients from 33 AML patients (24.2%) including 1 of M(1), 3 of M(2), 1 of M(4) and 3 of M(5). The NPM1 gene mutations were found in 7 out of 19 patients with normal karyotype and their incidence was significantly higher than that in patients with karyotype abnormalities (1/14, 7.1%, p < 0.005). The proportion of bone marrow blast cells and the count of peripheral white blood cells in patients with NPMI exon 12 mutation were higher than that in patients with wild type NPMI gene. It is concluded that the occurrence of NPM1 exon 12 mutations is observed more in AML patients with normal karyotype. NPM1 mutant cases are associated with more high amount of boon marrow blast cells and peripheral white blood cell count.