Idiopathic (genetic) epilepsy is a common neurologic disorder of dogs and 25%-30% of these dogs are refractory to antiseizure drug therapy. The purpose of this open-label clinical trial was to evaluate the potential efficacy and tolerability of a traditional Chinese herbal formula Di Tan Tang as an add-on therapy for dogs with refractory presumptive idiopathic epilepsy. Eight dogs with refractory presumptive idiopathic epilepsy were evaluated for seizure frequency 3 months prior to and 3 months after instituting oral Di Tan Tang therapy (0.5g/10lbs body weight, q 12 hrs) using a prospective open-label, non-comparative clinical trial design. The overall mean reduction in seizure frequency after treatment with Di Tan Tang for the 8 dogs was significant (p=0.035) at 27%, with 2 dogs qualifying as responders (≥50% reduction in seizure frequency). One dog experienced mild sedation after starting Di Tan Tang; no other adverse effects were recorded for the remaining dogs. The results of this preliminary investigation suggest that Di Tan Tang may be a useful adjunctive treatment option for dogs with refractory epilepsy. Further clinical investigation into the potential use of Di Tan Tang in canine refractory epilepsy is warranted.