Abstract. Let G be a group and let p be a prime number. If the set A(G) of all commuting automorphisms of G forms a subgroup of Aut(G), then G is called A(G)-group. In this paper we show that any p-group with cyclic maximal subgroup is an A(G)-group. We also find the structure of the group A(G) and we show that A(G) = Autc(G). Moreover, we prove that for any prime p and all integers n ≥ 3, there exists a nonabelian A(G)-group of order p n in which A(G) = Autc(G). If p > 2, then A(G) ∼ = Zp × Z p n−2 and if p = 2, then A(G) ∼ = Z 2 × Z 2 × Z 2 n−3 or Z 2 × Z 2 .