Dislocations in ceramic oxides are drawing increasing attention owing to their promising properties, including dislocation-tuned electrical conductivity, thermal conductivity, and electro-mechanical properties as well as enhanced fracture toughness damage tolerance.  However, due to the brittleness of most oxides at room temperature, it remains a great challenge to engineer dislocations without forming cracks, which is a prerequisite for harnessing these promising properties.  From the aspect of mechanical deformation, nano-/micromechanical testing is a feasible approach to achieve this goal.  Here, we first demonstrate that dislocations can be effectively introduced into various ceramic oxides (e.g., SrTiO₃, BaTiO₃, TiO₂, and Al₂O₃) at room temperature by using nanoindentation pop-in stop tests. Interestingly, we find a size-dependent competition between purely dislocation-dominated plastic deformation under a critical indenter tip radius and a concurrent appearance of cracks and dislocations when the tip radius is larger than a certain value.  We further extend the deformation scale up to the millimeter regime using Brinell indentation and identify a reversal of the above size-dependent competition.  We will address the underlying mechanisms by examining the dislocation nucleation, multiplication, and motion individually to shed new light on the dislocation mechanics in oxides at room temperature.