In rat brain slices, the Kv channel blocker 4-aminopyridine (4-AP) induces seizure-like events. This effect is absent in slices from chronic epileptic rats generated using the kainic acid model. The reason for this phenomenon remained elusive as an altered expression level of Kv channels was ruled out as a mechanism. We recently described that the Ile400Val RNA editing of Kv1.1 generates 4-AP–insensitive Kv1 channels (Kv1.1I400V). We therefore hypothesized that altered RNA editing levels account for the reduced ictogenic potency of 4-AP in chronic epileptic rats. We found fourfold increased RNA editing ratios in the entorhinal cortex of chronic epileptic animals compared to healthy control animals. Electrophysiologic recordings in Xenopus oocytes revealed that the observed increased Kv1.1I400V editing level can in fact lead to significant loss of 4-AP sensitivity. Our data suggest that altered Kv1.1I400V RNA editing contributes to the reduced ictogenic potential of 4-AP in chronic epileptic rats.