This paper studies the security of the block ciphers ARIA and Camellia against impossible differential crypt- analysis.Our work improves the best impossible differential cryptanalysis of ARIA and Camellia known so far.The designers of ARIA expected no impossible differentials exist for 4-round ARIA.However,we found some nontrivial 4-round impossible differentials,which may lead to a possible attack on 6-round ARIA.Moreover,we found some nontrivial 8-round impossi- ble differentials for Camellia,whereas only 7-round impossible differentials were previously known.By using the 8-round impossible differentials,we presented an attack on 12-round Camellia without FL/FL~(-1)layers. This paper studies the security of the block ciphers ARIA and Camellia against implicit differential crypt-analysis. Our work improves the best impossible differential cryptanalysis of ARIA and Camellia known so far. The designers of ARIA expected no impossible differentials exist for 4-round ARIA. However, we found some nontrivial 4-round impossible differentials, which may lead to a possible attack on 6-round ARIA. Moreover, we found some nontrivial 8-round impossi- ble differentials for Camellia, only only 7-round impossible differentials were previously known.By using the 8-round impossible differentials, we presented an attack on 12-round Camellia without FL / FL ~ (-1) layers.