Article 163 of the Korean Patent Act prohibits the re-trial of a final and conclusive decision based on the same facts and evidence as an earlier case. In a recent Korean Supreme Court decision, the Supreme Court clarified its previous decision and held that the doctrine of res judicata should be reviewed at the time a final and conclusive decision is rendered in the second (or subsequent) case.

In 2012, the Supreme Court, in an en banc decision, held that res judicata exists only if one case has been finally decided and concluded. If the earlier case has been concluded, then the facts and evidence from the earlier case should be compared with the facts and evidence from the second (or subsequent) case at the time of filing the petition for the subsequent case (Supreme Court Decision No. 2009Hoo2234 rendered on January 19, 2012). 

In its recent decision, however, the Supreme Court held that the doctrine of res judicata should be reviewed at the time the decision is rendered in the subsequent case rather than at the time of filing the petition in the subsequent case (Supreme Court Decision No. 2018Hoo11360 rendered on April 9, 2020). In this recent case, the IPTAB had dismissed a petition for violating the doctrine of res judicata. The petitioner appealed to the Patent Court while also raising new invalidation grounds that were not raised in the IPTAB petition (i.e., lack of novelty and violation of description requirements). The Patent Court confirmed that the petition violated the doctrine of res judicata since it should be applied at the time of filing the petition. Moreover, the Patent Court indicated that since res judicata was evaluated at the time of filing the petition, additional facts and evidence submitted to the Patent Court would not affect the res judicata analysis. The petitioner appealed the case to the Supreme Court.

In its ruling, the Supreme Court stated, "[a]lthough the petitioner cannot change the subject matter of the petition, it is allowed to amend the grounds for the petition under Article 140(2) of the Korean Patent Act. Thus, the IPTAB should determine whether the petition for trial violates the doctrine of res judicata at the time the decision is rendered. Accordingly, the IPTAB should consider all the facts and evidence submitted from the filing of the petition to the rendering of the decision to determine whether the petition is based on the same facts and evidence as in the previous final and conclusive decision." (Supreme Court Decision No. 2018Hoo11360 rendered on April 9, 2020). In other words, res judicata can be determined by comparing the facts and evidence of the two cases only after completion of both cases. However, the Supreme Court also indicated that only the facts and evidence that were made at the IPTAB stage can be used for comparison.

Thus, if an earlier ruling has been made on a particular patent, the petitioner in the subsequent petition is encouraged to review the earlier decision and make sure to submit new facts and evidence at the IPTAB stage.