Myeloid leukemia (ML) is heterogeneous cancer classified by abnormal growth of myeloid cells due to genetic aberrations and mutations. It is generally categorized by clonal disorders of hematopoietic stem cells and differentiation. The molecular mechanism behind the myeloid malignancies is not yet known, but recent sequencing analysis reveals all the mutated factors. As we know that there is currently no compromise on therapy for such types of malignancies and at the present painful process like chemotherapy and radiation therapy are not effective for the treatment of ML, so there is an urgent need to develop a non-invasive biomarker for different types of ML. MicroRNAs (MiRNAs) is a small non-coding RNAs that have been involved in a wide range of biological function and it is the main cause of the manifestation of many diseases. Among the reported MiRNAs, MIR-21 is considered to be an important MiRNA, which is frequently elevated in many types of types of cancer, suggesting that it plays an important role in cancer progressions. So far, there is no paper that signifies the role of miR-21 in all types of ML and the number of studies on the different category of ML is sparse. Therefore, the main thrust of this paper is to provide an overview of the current clinical evidence and significance of miR-21 in ML. It was found that MiR-21 was found to be normally upregulated in all types of ML, however, we summarize the important research findings surrounding the role of miR-21 in different types of ML.