To better understand the internetworking of different biological mechanisms working in a human body, it is essential to first establish a fundamental knowledge of the biological pathways. In this paper, a knowledge representation scheme for biological pathways is presented and discussed. First, the high level modeling concepts involved in this scheme are explained using a simple status-activity diagram. Detailed knowledge representation of a biological pathway is then investigated and discussed using a class-based approach. The proposed knowledge representation scheme is simple yet comprehensive enough to cover any types of biological pathways.