I experimentally analyzed the effect of fire season on small mammal and arthropod biodiversity in shortgrass steppe. Arthropods and mammals play important roles in the functioning of shortgrass steppe, serving as decomposers, pollinators, herbivores, predators or prey- cycling nutrients and forming important links among trophic levels. There is a lack of research that directly addresses the effects of fire season on animal communities in shortgrass steppe. Studies in other ecosystems have indicated animal species, populations, and communities respond differentially to disturbance by fire. The magnitude of the response depended on the vagility, life history and trophic level of the animal, and the timing, extent, and intensity of the fire. My study site was in the southern Great Plains on the Kiowa National Grassland. My experimental design was completely randomized, with 3 treatments and 4 replicates per treatment. Treatments were dormant-season fire in April, growing-season fire in July, and unburned. Response variables were small mammal and arthropod species richness, abundance, and relative abundance. Fire treatments were applied in 1997, and response variables were measured repeatedly for four years from 1997 through 2000. Data were analyzed with SAS MULTTEST ( = 0.05). Arthropod species richness significantly differed among treatments; growing-season fire plots had a significantly higher number of beetle species (P = 0.04) than unburned or dormant-season fire treated areas. However, beetle abundance did not significantly differ among treatments. Significant differences were never detected in overall rodent species richness or abundance among treatments through time. However, three rodent species did respond differentially to fire season, with Onychomys leucogaster being relatively more abundant and Reithrodontomys montanus being relatively less abundant on fire-treated plots, and Spermophilus tridecemlineatus apparently unaffected by fire. Relative abundance patterns of both small mammals and arthropods generally paralleled those of species absolute richness and abundance.