HbE/β-thalassemia is the most common severe form of thalassemia particularly in SEA region including Malaysia and globally, it comprised of a significant severe form of β-thalassemia disorder. It has various clinical manifestations ranging from very mild anemia to severe manifestation similar to beta thalassemia major. Many different syndromes are observed in HbE/β-thalassemia. Several genetic modifiers have been reported to play important role in contributing to phenotypic variability. The true reasons underlying this phenotypic variability remain unknown. The most reliable predictive factor of the disease phenotype is the nature of the beta globin gene mutation itself. However, the degree of severity is also believed to be affected by other genetic modifiers. For instance, high HbF level ameliorates the clinical severity of β thalassemia patients. Therefore, identification of these genetic modifiers is very important. The association of severe clinical manifestation and the specific β-globin gene mutation has been known. But the wide scope and other potential predictors have been only recently appreciated. This review therefore aimed to reveal the potential genetic modifiers of HbE/βthalassemia patients based on the previous reported studies. A better understanding on the mechanisms underlying the variety of phenotypes of this disease may lead to the direction for a better future management plans. This also promotes “personalized medicine” in patient care.