The purpose of this study was to develop an instrument to assess the physical aspects of classroom environment in Malaysian secondary schools from the students’ perspective. Constructs and items of the instrument were identified through review of literatures, interviews with teachers and analysis of existing instruments on the physical aspects of classroom. The instrument was validated by seven experts in the field of education. A total of 900 students are involved in determining the reliability of the instrument. As a result, an instrument with six main constructs, namely furniture, facilities, space, lighting, indoor air quality and colour were developed. The instrument was in the format of five-point Likert scale, ranging from 1 which represents strongly disagree to 5 which represents strongly agree. The factor loading of each item ranged from 0.45 to 0.93 and the value of reliability (alpha) for each construct ranged between 0.881 and 0.940. The findings of the study showed that the instrument had high validity and reliability and can be used to assess the physical aspects of classroom environment in secondary school.