Abstract The blast phase in chronic myelogenous leukemia (CML) is associated with mutation of several genes. It is well known that p53 gene mutation plays a key role in the myeloid or lymphoid blast phase of CML. But for the case of the N-ras gene, the association between N-ras mutations and the blast phase of CML is not yet known. We report here on a case of detecting N-ras point mutation without p53 mutation in a 64 year-old man who suffered from the lymphoblastic blast phase of CML.