Reading-integrated writing is known as an effective approach to teaching and learning vocabulary as it allows students to transfer vocabulary from a source text to writing. This study examines whether vocabulary transfer from an input text to writing varies according to the two types of tasks: essay writing and synchronous text chat. One hundred Korean college students from four "Reading and Writing" classes performed both tasks, and their vocabulary use was compared between the two tasks. The tokens and the types of words used in essay writing and chatting were compared against a base wordlist constructed from the input text, and their lexical profiles were analyzed using various programs, such as RANGE, VocabProfile, and WordSmith. The findings show that more varied words were transferred from the source text to the chat scripts than to the essays. While the lexical diversity was slightly greater in the chat scripts than in the essays, the difference was not statistically significant. Interestingly, the chat scripts exhibited the same level of lexical density (i.e., the ratio of content words to function words) as the essays. It can be inferred from the findings that the synchronous chat provides a valuable context for practicing target language, and that it is as useful as essay writing for promoting vocabulary transfer from reading to output production. In addition, the findings suggest that reading can become a beneficial source of language input that leads to output production.