The branching structures found in biological systems have evolved to an optimum arrangement that distributes nutrients efficiently in the system. Since the flow fields of polymer electrolyte membrane (PEM) fuel cells serve similar functions to the nutrient transport systems in plants and animals, it is expected that flow fields with a similar hierarchical structure could optimize the transport efficiency of reactants and improve the performance of fuel cells. In this paper, a series of bio-inspired flow field designs inspired by the venation structure of a tree leaf is developed. Two different configurations, interdigitated and non-interdigitated, are considered in implementing the hierarchical structures. Murray's law, which describes the optimum configuration found in biological circulatory systems, is used to determine the flow channel widths of different generations. The bio-inspired design using Murray's law is compared to a design with constant channel width. Both numerical and experimental studies are carried out to investigate these bioinspired designs. The mass, velocity, and pressure distributions within the channels and the gas diffusion layers, as well as the fuel cell performance, are studied for different flow field designs. The results show that the bio-inspired interdigitated designs substantially improve the fuel cell performance by 20-25% compared to the conventional designs. Copyright (c) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.