In recent years, marine science education has received increasing attention around the world, but the integration of STEM education into the marine curriculum is rarely applied to lower-secondary schools. The purpose of this research was to determine the effect of a teaching module on the topic of marine science, developed using a STEM approach, on the motivation, interest, and marine science achievements. The 9th-grade students from two classes in a Taiwanese public school were recruited in this study. Students in the experimental group were taught using the STEM course. Students in the control group were taught in a traditional didactic teaching course. Pre- and post-tests were used to determine marine science achievement, interest, and learning motivation. The experimental group gained significantly superior scores in three out of four dimensions towards motivation and two out of three dimensions interest. A significant difference was found between the experimental group and the control group, with the former showing increased marine science achievement over the latter in higher-order thinking; however, no significant differences were with respect to cognition. It is concluded that involving STEM-based implementations in teaching, the subject "Marine Science" increases the success rate and attitude towards the subject of students.