Individuals affected by autism spectrum disorders (ASDs) exhibit affective symptoms such as enhanced anxiety, which has been seen in rodent models of ASDs as well. Exposure to stress is also known to be anxiogenic. However, the effects of stress on animal models of ASDs remains less explored. Hence, in the present study we examined the impact of acute foot shock stress on anxiety-like behavior in two monogenic rat models of ASDs, fragile X mental retardation 1 knockout (Fmr1) and phosphatase and tensin homolog heterozygous (Pten). Before exposure to stress, the basal levels of anxiety-like behavior in both Fmr1 and Pten rats were comparable to that seen in wild-type (WT) control rats in an open-field arena. After exposure to the foot shock stress, however, Fmr1 rats showed the highest levels of anxiety-like behavior. WT animals also showed enhanced anxiety-like behavior but not as robustly as the Fmr1 animals. In Pten animals, on the other hand, the same stressor did not elicit any anxiogenic effects. In a separate group of rats, the efficacy of the acute foot shock in triggering a stress response was confirmed wherein a comparable surge in circulating corticosterone was seen in all three experimental groups. Thus, the same acute stress led to different effects on anxiety-like behavior in different rodent models of ASDs, suggesting that vulnerability to stress-induced changes in anxiety may vary with the underlying genetic mutations.