Two enzymes, thrombin and transglutaminase, both participate in the formation of fibrin networks and contribute to the mechanical strength of biogels. A theoretical model built from the available kinetic data showed that a competition may take place between the two enzymes for their common substrate, fibrinogen. To evidence this phenomenon experimentally, the concentrations of the reactants were varied and the rheological properties of the resulting fibrin gels explored. The elasticity of the gels was not a singular function of the transglutaminase concentration, the optimum being also related to fibrinogen and thrombin concentrations. Thrombin concentration influenced the kinetics of gelation, but not the evolution of the mechanical properties of the gel. An indirect relationship between gel elasticity and thrombin concentration was observed upon covalent binding. The liquid phase inside the gel contained a high amount of soluble proteins when a high transglutaminase concentration was used. The impact of this competition between the two enzymes, demonstrated here for the first time, is evaluated for biomaterial elaboration.