Chronic myelomonocytic leukemia (CMML) is a malignant hematopoietic stem cell disorder with clinical and pathological features of both a myeloproliferative neoplasm (MPN) and myelodysplastic syndrome (MDS). CMML is characterized by peripheral blood monocytosis accompanied by bone marrow dysplasia; cytopenias and hepatosplenomegaly are common. The pathogenesis of CMML is poorly understood. CMML arises by the serial acquisition of somatic genetic events that create multiple, distinct neoplastic cell clones. Transformation to acute myeloid leukemia (AML) is a well-known phenomenon and reaches 15-20% of cases. However, we report here a rare type of transformation to B cell acute lymphoblastic leukemia (B-ALL) in a 71-year-old female. There is a paucity of case reports on this particular transformation where only one case in adults and another case in a 10-month-old infant. The transformation of other subtypes of MDS such as refractory anemia with or without sideroblasts and or with increased blasts to B-ALL has been reported in the past. It is not very clear if there is a specific provocative factor for this particular transformation since the cytogenetic and molecular markers in our patients were all negative except pathogenic variants in the NRAS and TET2 genes at high allele frequencies on retrospective analysis. The new lymphoid malignancy /clone for our case was cleared after 2 cycles of mini HCVAD protocol. We focused our treatment on this new lymphoid clone which was cleared after 2 cycles of mini HCVAD protocol. Although the transformation of CMML into B-ALL is a rare complication, we believe further analysis or cohort study on larger CMML cases to elaborate more on the risk factors, cytogenetic and molecular events that might contribute to such complication.