This study aimed to explore the learning effects of the online course of applying case method teaching to making friends on the Internet for sixth graders. This study adopted the quasi-experiment design. The subjects were fifty-three students who were divided into the experimental group and the control group. The online course combined case method teaching with the discussion forum to support students' learning. The main findings included (1) The experimental group had a significantly higher score of knowledge of making friends on the Internet than the control group did. (2) The experimental group had a significantly higher score of behavioral aspect of making friends on the Internet than the control group did. (3) The experimental group had higher satisfaction and positive attitude toward the online course. (4) The online discussion could help the students to enhance their awareness on dangerous signs and find out the solutions related to making friends on the Internet.