Ultra-compact nuclear rings (UCNRs) can be defined as those galactic circumnuclear rings with a radius inferior to 200 parsecs [1]. Because very high spatial resolution is needed, this population has not been studied systematically until now. One important issue that has to be solved is whether UCNRs have an origin similar to larger circumnuclear rings, which are related to inner Lindblad resonances, or whether they have a different origin. We present the first results of a survey performed on 487 galaxies imaged by HST, to find and characterize UCNRs. These results include the detection of new rings as well as the confirmation of rings that were already known. We present a list of 23 reliably detected UCNRs and discuss their origin.