In order to consider the effect of salt dissolubility on miso quality, we produced miso using salt of different particle sizes. By comparing the chemical constituents of miso produced with salt of different particle sizes over 20 days from the start of preparation, we found that the amount of amino acids increased and sugar decreased in miso that was produced using salt with a large particle size. At approximately 50 days of aging, the effect of salt particle size on miso quality decreased. However, a difference in the color of the miso due to a difference in the salt particle size was observed after aging for 50 days. The findings suggest that miso with a strong red color can be produced using salt with a large particle size. In addition, the diffusion behavior of the salt in the raw materials of the miso during the aging process was examined using a conductivity meter. As the NaCl concentration in the miso increases, conductivity also increases. Although the conductivity meter used in this experiment is usually used to measure conductivity in a liquid, the possibility of determining NaCl concentrations in the miso, which is a paste, was suggested. The findings showed that estimating the dissolution and diffusion behavior of salt during the miso aging process was possible using a conductivity meter.