In this paper the automorphism group of two posets, D k,n and B m,n is determined. D k,n is the poset of DNA strands of length at most n, built up with k complement pairs of letters, and partially ordered by the subsequence relation. B m,n is the set of all subsequences of the word u m,n = a 1 ...a n defined over the alphabet {0, 1, ..., (m−1)}, where a i ≡ i (mod m). The automorphism group of B m,n was known already (see Burosch et al. [1]), here a short proof is presented as an illustration of the method used in the first part.