The main purpose of this study is to verify the effects of online pre-learning on high school students' English language achievement and motivation. A total of 60 high school English learners were selected and divided into experimental and control groups. This experiment was conducted over 10 weeks with 7 sessions. The results of the experiment revealed that there was a statistically significant difference in the change between the post-achievement score and the pre-achievement score of the control group and that of the experimental group, in favor of the experimental group. There was also a significant difference in the motivation of ‘globality' between the two groups. The results indicated that online pre-learning improves students' English language achievement and develops the motivation of ‘globality.' The results imply that it is necessary to conduct online pre-learning activities for the improvement of English and development of motivation of Korean high school students. This study has limitations such as the limited number of subjects and period of the experiment. Therefore, various further studies related to this area are proposed.