The Coalition Structure Generation (CSG) problem is a partitioning of a set of agents into exhaustive and disjoint coalitions to maximize social welfare. The fastest exact algorithm to solve the CSG problem is ODP-IP (Michalak et al. 2016) . In this paper, we propose a modified version of IDP (Rahwan and Jennings 2008) (named MIDP) and an improved version of IP (Rahwan et al. 2007 ) (named IIP). Based on these two improved algorithms, we develop a hybrid version (MIDP-IIP) to solve the CSG

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... em. After a description of the new algorithm MIDP-IIP, the results of the experimental comparison against ODP-IP are provided. Our analysis shows that MIDP-IIP performs fewer operations than ODP-IP. In addition, MIDP-IIP reduced significantly many problem instances running times (11% to 37%). The optimal CSG problem formulation Coalition formation can be applied to many real-world problems such as task allocation, airport slot allocation, and social network analysis. ODP-IP (Michalak et al. 2016) algorithm is the fastest exact algorithm for the CSG to date in practice. Given a set of n agents A = {a 1 , a 2 , . . . , a n }, a coalition C i is a non-empty subset of A. A coalition structure (CS) over A is a partitioning of A into a set of disjoint coalitions {C 1 , C 2 , . . . , C k }, where k ∈ {1, . . . , n} is called the size of the coalition structure i.e. k = |CS|. In other words, {C 1 , C 2 , . . . , C k } satisfies the following constraints:1) The optimal solution of CSG is an optimal coalition structure CS * ∈ Π A . The set of all coalition structures over A is denoted as Π A . Thus, CS * = arg max CS∈Π A v(CS).