This study investigated submicron-sized bubbles, more precisely ultrafine bubbles (UFBs). The number concentration, size, and scattered light intensity of UFBs were measured by particle tracking analysis (PTA). The results showed that storage temperature had a significant effect, whereas the storage containers had little effect on the long-term stability of UFBs. It was found that the second-order aggregation rate equation could predict the stability of UFBs; however, there were some differences from the theory at high storage temperatures. The features of the PTA were also discussed in detail.