Graphic Organisers help students make valuable connections by cataloguing and patterning ideas in writing. This study aims to investigate whether there is any difference in the overall mean writing scores between two groups: the Experimental Group (using Graphic Organisers) and the Control Group (using the Conventional Method) in the post-test. This study employs a quasi-experimental design, with quantitative data used for data analysis. Bubble maps and tree maps were the Graphic Organisers used by the Experimental Group in learning ESL writing skills. The study consisted of 120 Form Four students (16 years old) from two schools in the District of Hulu Langat, Selangor. The sample consisted of 60 students in each group (Experimental Group and Control Group). The experiment lasted for eight weeks. A pre-test was conducted prior to the intervention, and the post-test was carried out at the end of the experiment. The instruments (pre-test and post-test) consisted of three types of writing tasks: email writing, directed writing, and extended writing. ANCOVA was used to analyse the data obtained from the pre-test and post-test. The results showed that the Experimental Group significantly outperformed the Control Group in their overall writing performance, particularly in the areas of content, communicative achievement, organization, and language. The Control Group had difficulty in their overall and the four areas of writing because the Conventional Method did not help them improve their performance. This study has pivotal pedagogical implications as it demonstrates that Graphic Organisers (Bubble maps and Tree maps) facilitate students in their ESL writing.