Recently, considerable progress has been made in developing a high resolution SPECT system for small animal imaging. However, it is a major challenge to further improve the resolution for the convectional pinhole system without decreasing the sensitivity to a level that is beyond applicable. In this work, we explore the use of a novel confocal micro-ring aperture collimator along with ultrahigh resolution CdTe pixel detectors for a microscopic SPECT imaging system that will enable one to achieve an ultrahigh resolution at relatively high detection efficiency. The micro-ring aperture has a ring shape opening with width ranging from 30μm to 150μm and diameter around 2mm. The micro-ring aperture could benefit the microscopic SPECT imaging in two aspects: firstly, an appropriate ring-width can be chose so that the projection overlapping between two resolution elements (the two closest points in object space that one wants to resolve) can be well-controlled to the two small cross-sections between the two ring shape profile. Secondly, even with a small ring-width (say 100μm), a micro-ring aperture could offer a reasonable open-fraction for incident gamma rays, and therefore a relatively good sensitivity. To evaluate the use of the micro-ring apertures for microscopic SPECT imaging, a stationary microscopic SPECT system is proposed. This system uses 32 micro-ring apertures and 8 highly pixelated CdTe detectors that provide an intrinsic resolution of 100μm. And a series of comparing simulation study between micro-ring aperture and conventional pinhole aperture are carried on. The image of resolution phantom shows that smaller hot rods are visible from the ring aperture than convection ring aperture at the same open fraction. In addiction, the imaging of digital mouse-brain from ring aperture gives more details than the pinhole aperture. Simulation results indicate that the novel micro-ring aperture likely provides a better image quality than conventional pinhole aperture, especially for ultra-high resolution SPECT system.