Sextans A and Sextans B are two dIr galaxies situated in the outskirts of the Local Group, in which both PNe and HII regions have been detected (Magrini et al. 2002, 2003). In spite of their similarity (in terms of mass, luminosity and metallicity) it is likely that the two galaxies had a quite different star formation history as indicated by the different amounts of stars in the various evolutionary phases, and also reflected in the different number of PNe and HII regions observed. We have obtained deep spectra of PNe and HII regions in these galaxies with VLT. Phisico-chemical parameters have been derived, minimizing the sources of uncertainties often present in this kind of studies, by measuring directly, and not assuming, the electron temperature.