We investigate the robustness of biological networks, emphasizing gene regulatory networks. We define the robustness of a dynamical network as the magnitude of perturbation in terms of rates and concentrations that will not change the steady state dynamics of the network. We find the number of dynamical networks versus their dynamical robustness follows a power law. We observe module robustness to increase with node degree in published gene regulatory networks. Finally, based on dynamical robustness, we propose a growth model for producing networks with power law degree distibutions.