The purpose of this study is to examine the effects of PBL and motivational styles of Turkish high school students' attitudes on biology courses and on their academic achievements. Experimental study was conducted with 120 students. ANOVA was used to interpret the data. The results of the study indicated that, method and motivational styles did not affect on the attitudes of high school students towards biology. This study showed that there was a significant difference between motivational styles of students who are the achiever and social. (C) 2010 Elsevier Ltd. All rights reserved.