Abstract : This paper describes the irreducible representation of all groups of order 8 through Great Orthogonality Theorem. Although this method is not as lengthy as using Burnside method, the same approach cannot be used for all type of groups since, there are exceptions for cyclic groups and direct product groups. In order to deduce the irreducible representations for groups using Great Orthogonality Theorem method, we identify the groups like C ,C x C and C 8 2 4 2 xC x C .