Seventeen years following the introduction and subsequent adoption of the Competency-Based Curriculum (CBC) in Tanzanian secondary schools, teachers continue to grapple with its implementation. This research, guided by the curriculum framework, aims to uncover the underlying issues hindering the seamless execution of CBC and explore the various strategies employed by Biology teachers to address these challenges. The study involved 32 participants, including heads of schools, heads of Biology departments, Biology teachers, and students. Data collection methods encompassed interviews, focus group discussions, document reviews, and observations, with thematic data analysis yielding significant insights. The findings illuminate that Biology teachers encounter several hurdles, including insufficient knowledge, to effectively implement CBC, irregular and inadequate staff training related to CBC, insufficient teaching and learning resources, and inadequate laboratory space for equipment storage. In response to these challenges, Biology teachers have resorted to improvisation for missing laboratory equipment and have leveraged neighbouring schools' and colleges' laboratories to facilitate biology practical sessions. In light of these findings, the study recommends the implementation of regular in-service teacher training programmes specifically tailored to CBC, alongside the provision of necessary teaching and learning resources. These measures are essential to facilitate the seamless execution of the CBC and enhance the overall educational experience.