Let OPn be the orientationpreserving semigroup on [n]. For an arbitrary integer r such that 2≤r≤n-1, the structures of the maximal regular subsemigroups of the semigroup K(n,r) were studied. Using MillerClifford theorem, the authors have proved thatK(n,r) has exactly two classes of maximal regular subsemigroups, i.e.:M(α)=K(n,r-1)∪(Jr\Rα); N(α)=K(n,r-1)∪(Jr\Lα), α∈Jr, where Jr={α∈OPn: | Im(α)|=r}, α∈Jr, Rα and Lα are the Rclass and L class containing α, respectively.