This paper aimed to examine the effectiveness of using Mentimeter, which is an online virtual platform to enhance the writing vocabulary among pupils. By using Mentimeter, they can access the platform to collaborate with their peers and teacher regardless of the time frame, geographical and self-confident factors. This collaborative discussion platform would expand pupils' word bank and understanding about the writing task; thus helping them in accomplishing their writing tasks. An action research based on Kemmis and McTaggart model was carried out with 40 pupils with a marginal passing rate by using pre and post-test, questionnaire and unstructured interviews. The findings showed a significant difference between the results of pre and post-test and positive feedbacks from the pupils. In conclusion, Mentimeter is an effective tool to enhance pupils' writing vocabulary. The results of this study may be beneficial to educators in employing Mentimeter in teaching of writing vocabulary. However, this paper is only focused on the effectiveness of using Mentimeter to increase the vocabulary of pupils in writing within the targeted group thus further study is needed to ascertain the efficacy of using Mentimeter and to generalise the findings to a larger population.