Nowadays, the necessity of designing proper differentiated tasks for mathematically gifted students is a remarkable subject in international literature and practice. In this design-based study, it was aimed to analyze and construct characteristics for designing differentiated tasks of mathematically gifted students. Through this design process, preliminary and prototyping phases were used as a general framework to reveal these characteristics as design principles of the study. Literature reviews, experiences of practitioners and needs analysis studies about suggestions and key points reflecting the characteristics of differentiated tasks were conducted in preliminary research phase. After this phase, initial form of differentiated tasks with draft design principles were applied in classrooms in try-outs and field test with 12 mathematically gifted students and 4 mathematics teachers of these classrooms. The data obtained through qualitative methods lead to three categories; initial design principles as characteristics obtained through preliminary phase, modifications for tasks, and final design principles as characteristics obtained through prototyping phase.