Stress relaxation behavior of chemically treated short sisal fiber-reinforced natural rubber composite was studied. The effect of bonding agent, strain level, fiber loading, fiber orientation, and temperature has been studied in detail. The existence of a single relaxation pattern in the unfilled stock and a two-stage relaxation mechanism for the fiber-filled composite is reported. The relaxation process is influenced by the bonding agent, which indicated that the process involved fiber-rubber interface. The rate of stress relaxation increased with fiber loading, whereas it decreased with aging.