The purpose of this study was to examine the influence of the environmental education modular curriculum on secondary school students' academic achievements and on their conceptual understanding. In the study, the case study method was used. The research sample included a total of 23 7th grade students (12 male and 11 female) who were determined with the purposeful sampling method and who were attending a secondary school in the city center of Gümüshane at the time of the study. In the study, as the data collection tool, achievement tests and semi-structured interview questions were used. In order to reveal whether there was a statistically significant difference between the pretest and posttest achievement tests, t-test, one of parametric tests, was applied. According to the results of the analyses, the environmental education modular curriculum had positive influence on the secondary school students' academic achievements as well as on their conceptual understanding.