Abstract. We present a collision attack on the hash function HAS-160 reduced to 53-steps. The attack has a complexity of about $2^{35}$ hash computations. The attack is based on the work of Cho etal. presented at ICISC 2006. In this article, we improve their attack complexity by a factor of about $2^{20}$ using a slightly different strategy for message modification in the first 20 steps of the hash function.