This study investigated and analyzed the implementation and the role of learning vocabulary using Basic 850 learning strategy on a group of international adolescent foreign language learners in task-based lessons, using writing tasks that would lend them into the acquisition of vocabulary. Using a descriptive qualitative design, data were elicited from English as a foreign language (EFL. The class was taught using potpourri of six lessons with one language skill which was writing. Data was analyzed descriptively and triangulated from transcript of interviews, written tasks, and questionnaire. A macro-analysis of six lessons integrating writing skill was carried out. A qualitative analysis of the data indicated that using Basic 850 English has helped them to recognize the patterns and structures of the language. The results also suggest that characteristics such as linguistic focus, type of feedback from peer interaction influenced both the writing and vocabulary learning process and its stressfulness. The findings from this study would have practical implications for English as Foreign language teaching and learning.