This study aims to determine teacher candidates' written argumentation quality with the help of various socio-scientific issues in the context of the human reproductive system subject. For this reason, a case study was conducted with 24 science teacher candidates studying at a state university in Turkey. Data was collected with a questionnaire involving five open-ended questions. The questions interrogated testing for genetic diseases before marriage, sugar-loading tests during pregnancy, designer babies, surrogacy, and consanguineous marriage. In the data-gathering process, the participants were asked whether they supported the given socio-scientific issue and to provide written arguments for each question. Data were analyzed using the content analysis and the framework introduced by Sadler and Fowler (2006). According to the results, teacher candidates’ support and argumentation levels varied with respect to the issue. The teacher candidates’ arguments dominated in justification with elaborated grounds for the second and fifth issues whereas justification with elaborated grounds and a counter-position level was observed in a higher percentage for the third and fourth issues. For future studies, it is recommended to design an instruction period to develop teacher candidates’ argumentation qualities on the issues addressed in this study paper.