Diabetes and prediabetes are overwhelming public health concerns in Bangladesh. However, there is a paucity of the literature examining and measuring socioeconomic inequalities in the prevalence of diabetes in Bangladesh. To provide reliable data and contribute to a nationwide scenario analysis, this study aims to estimate the inequality in prevalence of diabetes and prediabetes and to identify factors potentially contributing to socioeconomic inequalities in Bangladesh. This study used data from the latest Bangladesh Demographic and Health Survey (BDHS) 2017-18, a nationally representative survey. A regression-based decomposition method was applied to assess the socioeconomic contributors to inequality. The prevalence of diabetes and prediabetes were about 10 and 15% among Bangladeshi adults, respectively. Both diabetes and prediabetes were significantly associated with age, wealth status, suffering from overweight or obesity and administrative divisions of the respondents ( < 0.001). Respondents' household wealth status accounted for about 74 and 81% of the total inequality in diabetes and prediabetes in Bangladesh, respectively. Administrative region contributed 24.85% of the inequality in prediabetes and 12.26% of the inequality in diabetes. In addition, overweight or obesity status contributed 11.37% and exposure to television contributed 5.17% of the inequality in diabetes. Diabetes and prediabetes affect a substantial proportion of the Bangladeshi adult population. Therefore, these findings should be considered in the context of current and proposed policy decision making and for tracking its progression with economic development in Bangladesh.