This study assessed the effects of a one-day environmental education program, ”Wings in the Sky”, at Chih-Nan Nature Center, on sixth-grade students' environmental literacy. A nonequivalent control group design was used. Experimental group one (n = 78) received didactic instruction with teachers' explaining and questioning. Experimental group two (n = 115) received a method emphasizing role-play and simulation games. The control group (n = 105) did not receive any instruction at Chih-Nan Nature Center. The findings showed that the didactic instruction significantly promoted environmental knowledge only. However, the role-play method significantly promoted environmental knowledge, environmental sensitivity, environmental attitudes, internal locus of control, and environmental action. These effects were still maintained one month after the end of the program. Implications of the research findings for program development and instructional practice of Chih-Nan Nature Center are described.