The purpose of this study was to investigate the mediating role of 7th grade students' motivation toward learning science in the relationship between their science learning environment perceptions and science achievement. The correlational research design was utilized in this study and data were collected from 922 7th grade students using self-report questionnaires and a multiple-choice science achievement test. While motivation to learn science was regarded as self-efficacy, task value, intrinsic goal orientation, and extrinsic goal orientation, students' perceptions of the learning environment in science class were assessed by considering the components of constructivist learning environment such as teacher support, involvement, investigation, and equity. The results are discussed in relation to the features of classroom learning environment related to students' performance in science class. According to the results obtained from latent variables path analyses, it seems important that classroom learning environments which were arranged by means of the perspective of the constructivist learning environment increase students' science achievement directly and indirectly by increasing their motivation toward science.