This study aims to investigate pre-service science teachers' knowledge levels, practical experiences, and perceived competencies in teaching biodiversity at secondary school level. The study was conducted in Turkey with 151 pre-service science teachers, 50 of whom were first-year, 34 second year, 42 third year, and 25 fourth year during the fall semester of 2022-2023. An open-ended biodiversity concept test was applied to identify their knowledge levels, prior education experiences, and perceived competencies in teaching biodiversity. Descriptive statistics and content analysis results revealed that as the year level increased, the knowledge levels and experiences of the pre-service teachers increased as well, and in parallel, they perceived themselves as more competent in teaching the subject of biodiversity. When first and second year students were evaluated together, it was found that most of their answers were at a low level in terms of their knowledge about biodiversity. When the third and fourth grade teacher candidates' knowledge levels about biodiversity were examined, it was revealed that they were predominantly at a good level. As can be clearly seen, as year levels increased, the level of knowledge also increased. These results highlight the importance of theoretical and practical courses for content and pedagogical knowledge on the perceived competencies of the pre-service teachers in teaching biodiversity.Journal of Turkish Science Education 696 the variability among living organisms from all sources, including, inter alia, terrestrial, marine, and aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species, and within the ecosystems. Biodiversity is identified by the interaction of various factors that differ spatially and temporally. For instance, average climate and climate variability, resource availability and overall productivity of an area, biodiversity stock and diffusion opportunities or barriers, spatial heterogeneity habitats and intensity and interdependence of biotic interactions such as competition, predation, mutualism and symbiosis, and intensity and type of sexual reproduction and genetic recombination (Balcha & Dalle, 2007). DeLong (1996) stated that there was still no coherent definition of biodiversity; it was defined differently by different people and based on his own findings, he defined biodiversity as follows: Biodiversity is a state or attribute of a site or area and specifically refers to the variety within and among living organisms, assemblages of living organisms, biotic communities, and biotic processes, whether naturally occurring or modified by humans. Biodiversity can be measured in terms of genetic diversity and the identity and number of different types of species, assemblages of species, biotic communities, and biotic processes, and the amount (e.g., abundance, biomass, cover, rate) and structure of each. It can be observed and measured at any spatial scale ranging from microsites and habitat p...