This study aimed to contribute to the literature by focusing on the effects of the negotiations of sociomathematical norms perceived by students on mathematical process skills. Problem-based mathematical activities were implemented in the seventh grade from a public secondary school in Turkey over a ten-week period in the second semester. The data obtained from students' worksheets, video recordings, and interviews were analyzed descriptively and were presented depending on their nature. The results indicated that the negotiations of sociomathematical norms perceived by students contribute to the development of some mathematical process skills (communication skills, reasoning skills, verification skills, and creativity skills) while limiting the development of others (connection skills). Therefore, it can be said that it is important to design and implement mathematics learning and teaching taking into account the effects of sociomathematical norms perceived by students on mathematical process skills.