In this paper, we present some improved impossible differential attacks on large-block Rijndael whose block sizes are larger than 128 bits. First of all, we present some important observations which help us to significantly improve the impossible differential attacks on large-block Rijndael proposed by Nakahara-Pavão (ISC 2007). Then we introduce some new impossible differentials for large-block Rijndael. Utilizing these longer impossible differential distinguishers, together with the technique of changing the order of MixColumns and AddRoundKey operations proposed by Zhang-Wu-Feng (ICISC 2007), we can apply impossible differential attacks up to 7-round Rijndael-160, 8-round Rijndael-192, and 9-round Rijndael-224/256. As far as we know, except the attack on Rijndael-256, all the other results are the best cryptanalytic results on large-block Rijndael.