The oxide superconducting ceramic Ba₂YCu₃O₇ is sensitive to environmental degradation. The significant deterioration seen for specimens annealed in air may be attributed to the combined effect of H₂O and CO₂. It has been found that this degradation could be lessened by the densification of bulk superconductor prepared from co-precipitated oxalate powder. We also investigated the effect of processing and microstructual control on the critical current density of Ba₂YCu₃O₇. Materials sintered from co-precipitated powders showed sintered densities up to 98.5% of theoretical value and were composed of a large number of plate-like grains ( 20-100μm long, 5-10μm thick ).The critical current density of highly dense samples at 77K under zero magnetic field remained at 350 Acm^-2 probably due to the presence of micro-cracks. Jc of the lower density sample ( 90% ) was larger than that of the high density sample. This might be due to a decrease in a large number of micro-cracks.