Abstract | In this paper we consider the monoid $O_{m \times n}$ of all order-preserving full transformations on a chain with $mn$ elements that preserve a uniform $m$-partition and its submonoids $O_{m \times n}^+$ and $O_{m \times n}^-$ of all extensive transformations and of all co-extensive transformations, respectively. We give formulas for the number of elements of these monoids and determine their ranks. Moreover, we construct a bilateral semidirect product decomposition of $O_{m \times n}$ in terms of $O_{m \times n}^-$ and $O_{m \times n}^+$. |