This paper presents a model for power systems operation planning that aims to maximizing the voltage stability margin and also the economic dispatch, formulated as a bilevel programming problem (BPP). The objective is to obtain a solution for the network operation planning that takes into account both technical and economical aspects. The bilevel model allows system operators to define different objective functions for maximizing the voltage stability margin and looking for an optimum economic dispatch, as well as permitting the imposition of constraints to both the variables of the inner and outer problems. The BPP is reduced to a single level optimization problem by replacing the inner optimization problem by its Karush-Kuhn-Tucker optimality conditions. This methodology does not require mixed-integer programming. Moreover, BPP formulation is simpler than other formulations, and it is also very flexible to accommodate the variables and control parameters. ©2008 IEEE. 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