This study explored the effect of writing activity on EFL participants’ speaking performance. In order to attain this purpose, three research questions were presented; 1) What are the characteristics of learners’ writing? 2) How does their speaking fluency change during the writing sessions?, and 3) What is the effect of writing practice on learners’ speaking fluency, in terms of features of spoken grammar? Four college students participated in this study. Pre- and post-oral proficiency test scores, the participants’ writing products, and recorded data of their speaking performance were used for data analysis. Results of data analysis showed that, first, the more proficient participants were, the fewer the errors they made in their writing. Second, there was an increase in scores of intermediate- and beginning-level of students between the pre- and post- oral tests while the scores of advanced level of students did not show any differences between those two tests. Lastly, the result shows that the learners with higher proficiency in writing ability have higher recognition to the spoken grammar. Pedagogical implications are also made on the effective teaching of English writing and speaking in the Korean classroom setting.