Formation of spinet phases in ZnO-Sb2O3 and ZnO-Sb2O3- Bi2O3 systems is studied by the use of X-ray diffraction. The formation of nonstoichiometric Zn2.33Sb0.67O4 phase is observed in both the systems at similar to900degreesC. However, in these systems, at higher temperatures (T greater than or equal to 1100degreesC), formation of the inverse spinet phase Zn7Sb2O12 is observed. The study has been extended to understand the effect of CrO3 doping on the stability of the different spinel phases in the previously mentioned systems. Interestingly, in both the systems, samples doped with CrO3, displayed the presence of Zn2.33Sb0.67O4 phase < 1200degreesC, indicating the stabilization of the spinel phase by CrO3.