<![CDATA[Teachers are professional educators whose duty is to educate, teach, guide, direct, train, assess, and evaluate students. Based on observations made in several high schools in Bantul, it is known that biology teachers still have difficulty understanding high school biology material. This study aims to determine in detail the internal and external factors that cause teacher difficulties in understanding Biology material, as well as to find out the Biology concepts in class X material that are difficult to understand by high school biology teachers in Bantul Regency. This research is a qualitative descriptive study. The research population was biology teachers at public and private high schools in Bantul Regency. The stages of the study included initial observation, preparation of research instruments, validation of research instruments, data validity testing, and data analysis. The instruments were arranged in the form of interview guidelines and questionnaires. Instrument validation was carried out by two validators who were experts in their fields. The validity test of the data carried out included testing the validity and reliability of the data. Data analysis includes data reduction, data presentation, and conclusions from the data. The results showed that several external and internal factors made it difficult for teachers to understand biology material. The external factors obtained are the lack of facilities and infrastructure, especially the tools and materials in the laboratory, and the difficulty in finding valid supporting information. Internal factors experienced are due to the content of the material that is difficult to understand, a large amount of material, the complex and abstract nature of the material, the number of foreign terms, and the wide scope of the material]]>
