Students understanding of science has always been of considerable importance in the area of science education research at school level. It tries to focus on issues such as tools to aid understanding, conceptual understanding, tools for evaluating understanding, individual knowledge structure of students so on and so forth. Concept map is one such tool that is used to elicit understanding the subject thoroughly as well evaluating knowledge and teaching- learning process success in a given domain. Concept maps are two- dimensional hierarchical and node-like diagrams that depict knowledge. This paper presents a view of using concept mapping as tool for eliciting students’ knowledge structure and evaluating understanding and teaching-learning process in science. This study used two different methods of evaluation- achievement test and concept map test- for evaluating students understanding.   The study depicts the  in the understanding and representation of concepts and propositions using concept maps as evaluation tool as compared to achievement test.