Superconductivity and microstructures of fluorinated and chlorinated YBa2Cu3Oz were investigated with BaF2 and BaCl2 as the fluorination and chlorination agents. The incomplete decomposition of BaF2 and BaCl2 led to inhomogeneous phase and elemental distributions as shown by energy dispersive analysis of X-rays (EDAX) and X-ray diffraction (XRD) analysis. A high (y ⩾ 2) chlorine concentration stabilized a tetragonal perovskite structure in the YBa2Cu3ClyOz compositions while an orthorhombic structure was observed in samples with a lower chlorine concentration. The maximum superconductivity transition temperature,Tc, was ⩽ 95 K in these fluorinated and chlorinated samples. Thus, our data are contradictory to the claims of high transition temperatures (155 K) recently reported for some of these compositions. The microstructural and phase composition data reported here could provide useful information in the search for possibly highTc phases in these fluorinated and chlorinated compositions.