The aim of the study was to determine the effects of biology project studies on gifted and talented students' motivation toward learning biology. In the study, "one group pretest-posttest" design is conducted. Study group consisted of 46 gifted and talented students participating in biology projects at two science and art centers (SACs) located at Marmara region in Turkey in the fall term of 2012-2013 academic year. The study group was selected through purposive sampling method. Biology projects were carried out by the students under the guidance of biology teachers in SACs. Qualitative and quantitative research methods were employed. Data were collected through Motivation towards Learning Biology Questionnaire as pre- and posttests and through semi-structured interview form after the biology projects were completed. While quantitative data were analyzed using descriptive statistics and paired sample t tests with SPSS 20, qualitative data were analyzed using content analysis method with ATLAS.ti 6.2 qualitative data analysis software. According to the study results, biology projects had a statistically significant negative effect on the students' motivation toward learning biology.