A natural number
m is called the homotopy minimal period of a map f : X → X if it is a
minimal period for every map g homotopic to f. The set HPer (f) of all
minimal homotopy periods is an invariant of the dynamics of f which is
the same for a small perturbation of f. In this paper we give a complete
description of the sets of homotopy minimal periods of self-maps of nonabelian
three dimensional nilmanifold which is a counterpart of the corresponding
characterization for three dimensional torus proved by Jiang and Llibre.
As a corollary we show that if 2 ∈ HPer (f) then HPer (f) = ℕ for such a
map.