The influence of solid loading of ceramic injection mouldings containing 45-60 vol % submicrometre zirconia powders on the green microstructure and sintering behaviour was investigated. The mouldings with lower solids content exhibit a coarser green microstructure, which, in turn, shows lower sintering activity. The sintering activity is largely improved by increasing the solids loading to 60% at which a sintered density of 99% theoretical can easily be attained at 1400 °C, which is primarily because of the evolution of a finer green microstructure. The green microstructure of the mouldings, along with the sintering behaviour, was found to be well correlated with the average pore diameter, rather than the most-frequent pore diameter in the pore-size frequency distribution of the green compacts. The moulded compacts, although containing considerable amount of agglomerates, show isotropic shrinkage behaviour.