Environmental pollution is considered to be one of the biggest problems nowadays and sustainable development is seen as its solution. Although this topic has been discussed more and more lately and the level of increased environmental awareness is noticeable, environmental behavior is still lagging behind. Education for sustainable development has been recognized as an important resource for raising environmental awareness, which encourages ecological behavior, and teachers are considered its key mediators. In accordance with this, the aim of this paper is to examine the knowledge and attitudes of teachers on the cross-curricular topic "Sustainable Development". For this purpose, a quantitative methodology and an online questionnaire of 21 statements were used, on the basis of which the respondents estimated the degree of their own knowledge and attitudes on the topic using a Likert scale. The results of the survey showed that more than half of the surveyed teachers understand the concept of sustainability and sustainable development. Although teachers consider this topic to be an important part of the educational system, only less than half of teachers believe that they are familiar with the cross-curricular topic "Sustainable Development". Slightly more than half of the surveyed teachers believe that they are competent in teaching this topic, while less than half of teachers attend professional development related to this topic. There is almost an equal number of teachers who claim that the school provides them with education and workshops on education for sustainable development, as well as the number of those who do not agree with this statement or are not sure about it. The results of the research have shown that class teachers are statistically more inclined to claim that they manage to include content from a cross-curricular topic in their subject area compared to subject teachers.