This study was designed to explore the effects of problem-based learning (PBL) strategies on the attitudes of female senior high school students toward integrated knowledge learning in science, technology, engineering, and mathematics (STEM). Content analysis and focus group methods were adopted as the research processes. Data and information about the STEM internet platform, an attitude scale and the contents of interviews were also collected for analysis. The subjects were 10th grade students at a girls' senior high school who volunteered to organize teams for a Solar Electric Trolley Contest. A total of 40 students were grouped into 18 teams. The results of the study indicate: (1) that PBL strategies can be helpful in enhancing students' attitudes toward STEM learning and the exploration of future career choices; (2) that the PBL teaching strategy helped to lead students step by step toward completing the contest's mission and to experience the meaning of integrated STEM knowledge; (3) that not only that students can actively apply engineering and science knowledge, but also that students tend to gain more solid science and mathematics knowledge through STEM learning in PBL; and (4) that PBL can enhance students' abilities and provide them experiences related to knowledge integration and application. Therefore, it is recommended that the curriculum at the girls' senior high school include more content related to specialty subjects to enhance their technological capabilities. In addition, a learning mechanism should be offered to aid advisers or teachers in strengthening students' integrated and systematic knowledge about STEM.