This study examines the effects of task presentation on L2 college students’ task motivation and on their acquisition of English grammar. Fifty-two university students with low English proficiency levels were randomly assigned to one of either the purpose or the no-purpose of task presentation groups with 13 pairs of students in each. A trait questionnaire and a task motivation questionnaire were used to gauge the learners’ general motivation towards English learning as well as their task-specific motivation. The learners’ knowledge of grammar was also measured through pre-, post-, and delayed tests. The findings of this study demonstrate that L2 learners’ task motivation was significantly influenced by different types of task presentation, showing the necessity of clear and purposeful task presentation in instructional settings. The results also reveal that learners in the purpose of task presentation group exhibited higher grammar knowledge gains in long- as well as short-term retention. Pedagogical implications were made based on the results.