This paper investigates the stability issue of a discrete-time control system, where a state-estimate feedback controller (SEFC), digitally implemented with a fixed-point format, is used. A tractable closed-loop stability related measure is derived with finite-word-length (FWL) implementation consideration of the controller. The optimal realizations of the SEFC are defined as those that maximize this measure and can be shown as the solutions of a nonlinear programming problem. A sophisticated optimization strategy is presented to provide an efficient method for solving this problem, and a numerical example is given to illustrate the design procedure.