Psychometric testing is a fundamental data collection method inpsychological research. In the field of psycholinguistics, researchers often rely on self-reporting or make assumptions about the participants’ language experience and ability. To overcome the subjectivity of these approaches, there is increasing use of vocabulary size test in bilingual research as language proficiency estimates to account for individual differences, such as yes/no vocabulary size tests (e.g., LexTALE: Lemhofer & Broersma, 2012), and multiple-choice vocabulary tests (e.g., Vocabulary Size Test: Nation & Beglar, 2007). Owing to the lack of freely available standardized measures in the Malay language, our lab employed the standardized yes/no vocabulary test format (e.g., Amenta et al., 2020; Brysbaert, 2013) to construct a Malay vocabulary size test – the LexicalTest for Malay Speakers (LexMAL). In this workshop, we will discuss the process of test construction, guided by psychometric principles. In addition, the steps involved in measuring reliability and validity will be demonstrated.