The aim of this research is to evaluate the factors affecting biology lesson motivation of high school students. The data of this research are collected by using "Biology Lesson Motivation Questionnaire" and " Personal Information Form". At the end of the research, there is a significant difference between the level of students' biology lesson motivation and students' sex. On the other hand, there is not a meaningful difference upon the sex of the biology teacher and class levels. Morever, it is determined that effect greatness of students' sexes and classes on the level of biology lesson motivation is high and the effect of teachers' sexes is medium. (C) 2010 Elsevier Ltd. All rights reserved.