The potential of fluorescence technology for monitoring Miyauchi Iyokan citrus during post-harvest treatment was investigated in this research. Citrus fruits were harvested when still a greenish-yellow color with a low soluble solids (SS)/acid ratio. Dark storage of fruits at 80-90% of RH and 6-10°C for sixty days is expected to increase the quality of the fruits (becoming reddish orange in color and having a high SS/acid ratio). However, monitoring the quality during the treatment is substantial. In general, farmers monitored the quality by seeing the appearance, however, this way is subjective. Thus, the fluorescence technique was proposed since it was objective, relatively cheap and easy to apply. Two main fluorescence compounds from peel, polymethoxylated flavones (PMFs) (Ex. 370 nm/Em. 540 nm) and tryptophan-like (Ex. 260 nm/Em. 330 nm) compounds were found, and PMFs were used in this research since it is an essential constituent for the fruit quality. This work demonstrated that during treatment bright yellow color (suspected PMF compounds) had appeared when excited under 365 nm with UV-light from the beginning of storage period until day eighty, however, day fifty and sixty showed stronger intensity. Furthermore, SS/acid ratio reached the highest peak in day sixty. In addition, on day sixty an unpleasant odor appeared, which might be related to the off-flavor condition of metabolic excess. These results demonstrate the potential of fluorescence to monitor citrus fruit quality changes during postharvest treatment.