States have different ties to warring parties in armed conflict. Bias, as in being closer to one conflict side, is a known factor that shapes mediation processes. However, its particular role has been insufficiently studied. This study assesses bias as a significant influence on mediation in Ukraine. Armed conflict in Ukraine has been mediated by different actors, among which the Organization for Security and Co-operation in Europe (OSCE) launched a Special Monitoring Mission (SMM) to support mediation through impartial fact-reporting. This thesis examines the OSCE’s declared impartiality. This is done through a content analysis of interpretative statements by OSCE states about the SMM’s mandate and extensions. These 45 statements cover the conflict years 2014 to 2021 and form the material for the analysis. The study’s findings show that states’ interpretative statements hold bias in favour and disfavour of warring parties. Particularly favour for Ukraine and disfavour of Russia is apparent. Therefore, the OSCE does not speak with one ‘impartial’ voice but rather harbours different perspectives that potentially influence the organisation’s mediation efforts. The findings have implications for scholars and practitioners of international mediation alike.