The Genre-Based Approach (GBA) is a teaching writing method that has been discussed recently. Researchers and scholars have successfully employed GBA to help students practice writing in various contexts. The present study aims at investigating the use of the genre-based approach (GBA) and its effects on the writing achievement and attitudes of Thai engineering students. The sample consisted of 40 fourth-year engineering students who were enrolled in an English for engineering course. The study subjects were divided into three groups (high, medium, and low) based on their pre-test scores. Three lessons, which were directly related to writing content concerning engineering work (request e-mails, enquiry e-mails, and reports), were provided in 12 sessions. The post-test, attitude questionnaire, and interview were administered at the end of the experiment. The results of a one-way ANOVA analysis revealed that the writing ability of students in all three groups improved after the experiment with statistical significance. As for their attitudes, the findings showed that the students were satisfied with the teaching method, activities, and exercises. More importantly, they felt more confident in writing.