This study examines Swedish upper secondary school teachers' gendered conceptions about students' mathematical reasoning: whether reasoning was considered gendered and, if so, which type of reasoning was attributed to girls and boys. The sample consisted of 62 teachers from six different schools from four different locations in Sweden. The results showed that boys were significantly more often attributed to memorised reasoning and delimiting algorithmic reasoning. Girls were connected to gamiliar algorithmic reasoning, a reasoning type where you use standard method when solving a mathematical task. Creative mathematical founded reasoning, which is novel, plausible and founded in mathematical properties, was not considered gendered.