Whilst particular infectious bacteria are well-established to be associated with hematological diseases, more recent interest has focused on the entire microbial community of mucosal surfaces. In particular, the link between hematology and the microbiota (defined as the total assemblage of microorganisms in a mucosal environment)/ microbiome (i.e. the entire ecological habitat, including organisms, their genomes and environmental conditions) is becoming more well-known. Dysbiosis, or a change in the microbiome, has been linked to the development of neoplasms, infections, inflammatory illnesses, and immune-mediated disorders, according to growing data. Microbiota may influence distant tumor microenvironment through a variety of methods, including cytokine release control, dendritic cell activation, and T-cell lymphocyte stimulation. There are numerous major implications to study the microbiome in patients with benign and malignant hematologic disorders. In this review, we investigated the structure and function of the microbiome in patients with benign and malignant hematological diseases. Chemotherapy and immunosuppressive agents used in treatment of these benign and malignant hematological diseases may cause or exacerbate dysbiosis and infectious problems. After understanding the importance of microbiota in hematological diseases, we think that use of probiotics and dietary prebiotic substances targeting microbiota modification aiming to improve hematological disease outcomes should be investigated in future studies.