In the present study, ultrafine-grained (UFG: grain size < 1m) HSLA and IF steels were investigated. The tensile test results showed that, because of different strengthening mechanisms, UFG HSLA steel represents finally better ductility than initially more ductile IF steel. The analysis performed in the present study is based on the mechanism of generation the dislocation structures and takes into account effects of precipitation and solid solution strengthening. The results of this analysis, implemented in FEM, enable to capture the moment of plastic instability of ultrafine-grained microalloyed steels. A good convergence of the proposed model was observed for the investigated steels. The fact that ductility, strengthening and deformation mechanisms are strictly connected to each other suggests that the proper use of their synergetic effect may be used to improve the ductility of UFG materials.