Abstract: Using fog droplets spectrometer data and conventional meteorological elements observed in 12 fog events in northern Jiangsu province during autumn and winter from 2015 to 2017, the microphysical characteristics and fog droplets spectra were analyzed for light fog, fog, heavy fog, dense fog and extremely dense fog. Dominant microphysical processes during fogs of different levels were discussed based on analysis of a long-lasting fog case. The results indicate that the droplets concentration and liquid water content increase significantly with the enhancement of fog level, while the droplets mean diameter and maximum diameter are similar for light fog, fog and heavy fog until the visibility decreases to less than 200 m, after which mean diameter and maximum diameter both show an obvious increase. When the visibility deteriorates, the average droplet spectra of the number concentration and liquid water content both are uplifted, and the big droplets with diameter greater than 10 μm grow notably from heavy fog to dense fog. The number concentration of fog droplets is mainly controlled by small droplets, and the liquid water content is affected by large droplets. The average liquid water content of fog droplets in Donghai county suburb is comparable to that in Nanjing, but the number concentration is only about half of that in Nanjing and the mean diameter is about 2.3 times of that in Nanjing. In the case study, condensation nuclei activation and subsequent condensational growth are the dominant microphysical process during the period of visibility decreasing from 1000 m to 50 m. However, the condensable water vapor is an important factor affecting the effect of the process, which can make the number concentration and the mean diameter show different correlations. When the visibility drops below 50 m, the effect of collision-coalescence process is remarkable. After sunrise, droplet evaporation appears and gradually reinforces.