Environmental science (ES) was introduced in Bhutan as an optional school subject for classes IX-XII to equip young people with the knowledge, values, and skills to protect the environment and promote sustainable and equitable use of natural resources in the pursuit of gross national happiness. Teachers are believed to play a crucial role in the effective implementation of ES, and this paper analyses Bhutanese teachers' views on how well they have been prepared to implement ES. The interview data from 14 teachers and six principals showed that limited qualifications and professional development in teaching ES have resulted in lack of confidence in teaching ES, lack of pedagogical content knowledge, and lack of clarity about the ES objectives. These results suggest integrating more knowledge about education for sustainable development (ESD) into teacher education program to adequately prepare teachers to teach ES if required and integrate ESD principles into other subjects.