This article presents the BAsic income in BELgium (BABEL) dataset on public opinion on the introduction of a universal basic income (UBI) in Belgium, collected through an online panel among a sample of 3000 respondents in spring 2021. The BABEL survey implements an innovative vignette experiment in which both the policy design (i.e., the benefit level, the universality) and the potential policy outcomes (i.e., effect on poverty, unemployment) of a UBI are set to vary randomly. This full factorial experimental design is appropriate to analyze the complex of process of opinion formation about a UBI which entails multiple considerations. Accordingly, the data enables researchers to assess the net effect of the different design characteristics and hypothetical outcomes, as well as the trade-offs people are (not) willing to make to support basic income. Additionally, the survey includes items about benefit recipiency, COVID-19, demographic characteristics, general welfare attitudes, behavioral intentions, and political opinion. These data are thus appropriate for examining which design or outcome factors are relevant in shaping support for a UBI as well as extensive subgroup analysis.