YBa₂(Cu_1-xFe_x)₃O_7-y (x≥0.03) shows a tetragonal X-ray pattern different from that of well-recognized high-temperature tetragonal phase. Phase transition was observed at around 600°C for all samples (0≤x≤0.05) in magnetic susceptibility, electrical resistivity and thermoelectric power measurements. Seebeck coefficients of the pure YBCO were negative below about 500°C indicating complex conduction mechanism in the compound.