Abstract
This research is an endeavor to investigate the writing development in the genre of instruction through the application of genre-based approach. The participants were 20 university students from non-English major at a private university in Bangkok. A naturalistic participant observation was applied to collect the qualitative data, which are the participants’ written outputs from the writing tasks. The findings revealed that the participants tended to improve writing ability for the creation of the contextual information to encounter the communicative purpose based on the instruction genre as expected. In detail, they acquired the capability in applying the appropriate text organization and relevant language features into their writing effectively.