This study aimed to explore mathematics teachers’ perceptions of professional development. The study involved two public secondary schools in Ilala Municipality, Dar es Salaam. This was a qualitative study based on case study design. The study involved fourteen (14) participants that were selected purposefully. Two (2) heads of the schools, two (2) Academic Teachers, two (2) heads of mathematics departments, and eight (8) mathematics teachers were equally involved from both schools. Interviews, focus group discussions, surveys, and document analysis methods were used in data collection. Both interviews and focus group discussion were audio-recorded by using a protected smartphone with password to ensure data security. The documents reviewed includes; school policies, school calendars, and mathematics departmental meetings’ minutes. The data collected were analysed thematically to identify and interpret key themes. The data analysis was based on the following steps: transcription, data reduction, presentation, and discussion of findings. Fictitious names were used for names of people and schools to ensure confidentiality and anonymity. The study revealed that teachers perceived professional development as formal programs to improve teachers’ quality that were time-consuming and costly, while informal professional development programs were overlooked by teachers and other educational stakeholders. The study recommends that, in order to improve teachers’ quality as intended in professional development, there is a need to raise awareness for both formal and informal professional development programs among teachers and a learning community as a whole.