This paper reports on an online distance learning course that emphasizes the improvement of the self-efficacy beliefs of in-service elementary school teachers in teaching biological concepts. The course utilizes digital educational content and Open Educational Resources (OERs) and focuses on the interaction, peer support, and peer teaching into an online learning environment. In the design framework of the course, we investigated the educational needs of teachers and took into consideration the findings of other studies. A total of 251 teachers were enrolled in the online distance learning course and 142 completed it. Quantitative and qualitative data was collected in November 2020 through the bio-STEBI-A instrument and the posts in the forums of the course. The quantitative results revealed an improvement in both subscales of bio-STEBI-A, which were also confirmed by the qualitative ones, that underline the course, thus contributing to the improvement of self-efficacy beliefs of in-service elementary school teachers in teaching biological concepts. Recommendations are made for future research.