Due to the results of Lewowicz and Tolosa expansivity can be characterized with the aid of Lyapunov function. In this paper we study a similar problem for uniform expansivity and show that it can be described using generalized cone-fields on metric spaces. We say that a function f : X → X is uniformly expansive on a set Λ ⊂ X if there exist ε > 0 and α ∈ (0,