This study aimed to examine the implementation of science curriculum focusing on secondary schools in Ethiopia. To achieve this, a mixed-methods research approach, with a convergent parallel design, was employed. Using simple random sampling and comprehensive sampling techniques, 240 science teachers, 60 school leaders and 320 students from 20 secondary schools were selected as participants. Data collection involved questionnaires and interviews, which were analysed both quantitatively--using frequencies, percentages, means and standard deviations--and qualitatively through thematic analysis. The results revealed that the implementation of the secondary school science curriculum was insufficient and did not adequately address the key factors that influence its success. Critical issues such as resource availability, key stakeholder involvement, the establishment of a conducive school environment and supportive external contexts were found to be inadequate. In light of these findings, recommendations are provided to improve the implementation of secondary school science curriculum.