Instructional design problems are one of the most complicated and ill-structured types of problems due to the dynamic nature of design problems and decision-making processes. Formulating instructional design solutions thereby requires teachers to possess adequate decision-making knowledge and skills and apply them to instructional design. This study investigated how pre-service teachers made formative instructional design decisions for technology integration. Through a formative design activity related to teaching and technology, the study identified factors that influenced pre-service teachers' design decision-making for technology integration as well as instructional approaches that can help pre-service teachers make design decisions. Based on the analysis of pre-service teachers' design journals, design artifacts, and survey results, we identified six themes in terms of design decision-making according to three metathemes: (a) emphasis on the design process, (b) collaborative design experiences, and (c) iterative decision-making during prototyping. Meanwhile, instructional approaches such as open-ended guiding questions, conjecture mapping, peer-reviewing, and reflective practices allowed pre-service teachers to take an active role in instructional design decision-making for technology integration. Implications for teacher education practices and instructional design decision-making are discussed.