Online learning is being widely spread out to all nations with the quick speed. But only a few studies investigated the effect of learners’ personality on online learning behaviors and performance. This study examined the power of predictability of the five factor personality (Neuroticism, Extraversions, Openness to Experience, Agreeableness, and Conscientiousness) on online learning activities(task management activity, task performance activity, social activity, and non-task activity) as well as online academic achievement with digital portfolios. From 67 students who took online Course in "A" University located in Seoul, Korea participated in the investigation for eleven weeks. Personality traits, online learning activities and academic achievement were measured throughout the course period. Results indicated that in the case of task management, conscientiousness positively and agreeableness negatively were significant predictors of online learning behaviors. For the task performance in online learning, conscientiousness predicted achievement significantly. For social activity, only conscientiousness was a significant predictive variable. Agreeableness was a variable to negatively predict the task activities and openness to experience was a variable to positively predict non-task activities. Finally, conscientiousness of learners’ personality predicted online academic achievement significantly. The findings indicate that online learning designers and instructors should support the environment in that the learners can have accountability of their learning. Also, learners should be encouraged to perform as many task activities as possible. The result of this study will contribute to predict personality of successful online learners, form effective high-quality learning environment and establish a guideline suitable for the relevant students. Also, it is necessary to study the correlation between learners’ personality and online learning activity aiming at diverse ages and classes in depth and in detail for the purpose of increasing the possibility of generalization. A study also should be carried out considering character of teams in online learning.