In this paper, we study all kinds of open sets introduced in bi-generalized topological spaces, namely, U(m,n)-semi open sets, U(m,n)-pre open sets, U(m,n) -regular open sets, , U(m,n) -open sets, , U(m,n) -open sets, , U(m,n) -open sets, (m, n)-open sets and quasi generalized open sets and investigate some of their properties. We choose , U(m,n) - semi open set as the bases open set for our investigation and compare the relationships between the , U(m,n) -semi open sets and other open sets in this bi-generalized topological spaces. U(m,n)