This study focuses on developing the abilities of preservice secondary mathematics teachers to modify mathematical tasks through noticing-oriented activities. To this end, the study designs three phases for Noticing-Oriented Task Modification Activity (NOTMA) and applies it to preservice secondary mathematics teachers. It investigates characteristics of preservice teachers' noticing that emerged from NOTMA and analyzes their modified tasks in terms of their noticing. The results indicate that the development of preservice teachers' noticing is linked to their progressive understanding of the mathematical and pedagogical elements involved in tasks, and this improvement influences their task modification. Based on the results, we discuss that NOTMA can be useful to develop the task modification abilities of mathematics teachers and make some suggestions for the teacher training programmes.