A coloring of a connected graph G is a function f mapping the vertex set of G into the set of all integers. For any subgraph H of G, we denote the sum of the values of f on the vertices of H as f (H). If for any integer k ∈ {1, 2, · · · , f (G)}, there exists an induced connected subgraph H of G such that f (H) = k, then the coloring f is called an IC-coloring of G. The IC-index of G, denoted as M (G), is the maximum value of f (G) over all possible IC-colorings f of G. In this paper, we present a useful method from which a lower bound on the IC-index of any complete multipartite graph can be derived. Subsequently, we show that, for m ≥ 2 and n ≥ 2, our lower bound on M (K 1(n),m ) is the exact value of it. . Research supported in part by NSC-102-2115-M-239-002.for 2 ≤ m ≤ n, in 2008, the problem regarding complete bipartite graphs was completely settled. In this present paper, we deal with complete multipartite graphs. A complete multipartite graph K m 1 ,m 2 ,··· ,m k is a graph whose vertex set can be partitioned into k partite sets V 1 , V 2 , · · · , V k , where |V i | = m i for all i ∈ {1, 2, · · · , k}, such that there are no edges within each V i and any two vertices from different partite sets are adjacent. A complete multipartite graph with k partite sets is called a complete k-partite graph as well. We also denote as K 1(n),m n+1 ,m n+2 ,··· ,m k , n ≤ k, the complete k-partite graphs in which there are n partite sets which are of size one and the rest (k − n) partite sets have sizes m n+1 , m n+2 , · · · , and m k . Therefore K 1(n) represents the complete graph K n .In this paper, we introduce some useful lemmas in Section 2. In Section 3, our main results are presented. We start with a useful proposition which gives a lower bound on the IC-index of the join of an independent set and a given connected graph. Consequently, a lower bound on the IC-index of any complete mutlipartite graph can be deduced. We shall show that our lower bound on M(K 1(n),m ) is indeed the exact value of it for m ≥ 2 and n ≥ 2. A concluding remark will be given in Section 4.