Elementary fatigue deformation mechanisms in duplex stainless steel bicrystals are studied by transmission electron microscopy (TEM). Attention is paid to the interaction between lattice dislocations and ferrite/austenite interfaces depending upon the orientation relationship (plastically compatible or incompatible) and the initial deformation (in the alpha-phase or in the gamma-phase). Furthermore, an attempt is made to understand the behaviour under mechanical solicitation of each phase in the bicrystal and to compare it with the single crystal deformation behaviour.