The stress relaxation behavior of an agar - gelatin mixture gel was analyzed as a function of the stress relaxation behaviors of the component agar and gelatin gels. A six-element model composed of three components of the Maxwell mechanical model was applicable for each stress relaxation behavior. Except for the behavior of the shortest relaxation time, the three elastic moduli of the mixture gel, including the instantaneous elastic modulus, became predictable from the corresponding moduli of the agar and the gelatin gels, taking into account the concentration dependence and using a parallel-series combination model for the elasticity. The viscosities of the mixture gel were also predictable from the corresponding viscosities of the component agar and gelatin gels, except for the behavior of the shortest relaxation time.