Attitude towards science (ATS) is a major concern in science education. Although many ATS instruments have been developed, they are based on different cultural systems and having some limitations. This study aims to validate an instrument for measuring students' ATS in Malaysia context. The instrument was adapted from Test of Science-Related Attitude, TOSRA (Fraser, 1981) and Attitude towards Science Measure, ATSM based on theoretical and research underpinnings. A total of 749 secondary school students responded to the instrument. Rasch analyses were performed to examine the psychometric properties of the instrument, including fit statistics, point-biserial correlations, person-item reliability and separation, and rating scale diagnosis. Data analysis indicated that the instrument exhibited satisfactory validity and reliability. This shows that it demonstrates sufficient evidences of psychometric properties and has the potential to be utilized as a diagnostic tool in assessing students' ATS.