Abstract: Based on aircraft observation data from the coastal areas of East China on September 23, 2023, combined with reanalysis data and the backward trajectory model, this study comprehensively analyzed the vertical distributions of aerosols, cloud condensation nuclei (CCN), and cloud microphysical properties to investigate the aerosol–cloud–precipitation interaction mechanism during a weak precipitation event. The main findings are as follows: (1) An elevated aerosol layer was observed at 1.5–3 km, with a peak number concentration (Na) of 6500 cm?3 and a uniform effective diameter (Da) centered around 0.11 μm. This layer coincided with the temperature inversion layer and cloud microphysical parameters indicated the presence of large particles likely remaining from evaporated cloud droplets at this level. Back trajectory analysis suggested that this high concentration aerosol layer may have originated from evaporated cloud droplets in upstream cloud regions. (2) The CCN activation spectra exhibited significant vertical variation, with aerosol activation characteristics transitioning from a marine–continental mixed type in the lower atmosphere to a cleaner continental type at higher altitudes. In addition, the aerosol activation ratio decreased exponentially with increasing aerosol concentration under the same supersaturation conditions. (3) High liquid water content (LWC, peak value of 0.79 g·m?3) coexisted with high cloud droplet concentration (Nc, exceeding 3000 cm?3) within the cloud. Notably, in regions where LWC exceeded 1 g·m?3, small droplets (Da <15 μm) accounted for more than 90% of the droplet spectrum, with no significant growth observed at the large-droplet end. This indicated that the cloud droplet growth was dominated by condensation, while collision–coalescence was suppressed, leading to the low precipitation efficiency. Overall, in this aircraft observation case under relatively clean conditions over the coastal East China, cloud evaporation may be an important source of the high-altitude fine-mode aerosol layer; meanwhile, the microphysical structure dominated by condensation processes within the cloud may have constrained the development of precipitation efficiency. This study provides valuable observational insights for understanding the aerosol–cloud–precipitation interaction under similar weak precipitation conditions in the coastal areas of East China.