Anger is a topic that requires intervention from teachers, counsellors, psychologists, parents, and all communities. The expressions of anger are subjective and sometimes hard to identify. Thus, anger should be measured more objectively, while the expressions need to be examined closely. The purpose of this study is to provide valid confirmation for development of an online instrument to measure the types of anger expression among adolescents. Data were collected from 935 adolescents from nine schools in northern Malaysia and the theoretical literature search. The data were analysed to provide evidence of construct validity in terms of item factor analysis, reliability estimates, and correlation between the types of anger expressions. Findings were used to develop an online Adolescent Anger Instrument. It measures five types of anger expressions, namely, physical, verbal, intrinsic, extrinsic, and passive. The results showed that the instrument is internally consistent with high evidence of construct validity. Exploratory factor analysis, with varimax rotation, suggested the existence of five distinct types of anger as conceptualised. Meanwhile, the correlation between types of anger expressions indicates the strength of the relationship between them. Discussions on the findings are provided, while suggestions for future research are also described.