Research has indicated the importance of representational competence for learning science. Issues related to the nature of students' representational competence, such as how they demonstrate representational competence across different domains of science, require investigation. In the present study, four aspects of representational competence across two domains of science were investigated: use of dynamic representations, use of multiple representations, use of adequate science concepts, and use of visualization strategies. Two instruments, the representational competence of states of matter and the representational competence of carbon cycling assessments were delivered via a computer-based drawing tool and were used to measure 40 senior high school students' representational competence for the topic of states of matter and carbon cycling. The results indicated that the representational competence demonstrated in one topic was not significantly correlated to that demonstrated in the other. The results of path analyses using multiple regressions indicated a trend that the extent to which multiple representations were employed was significantly and closely related to the extent to which appropriate science concepts were applied to make the drawings. Implications of the findings are discussed.