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During the past five decades, China has witnessed frequent fog and haze events. Previous studies have revealed that in polluted regions of East China, such as the Beijing-Tianjin-Hebei (BTH) region, the Yangtze River Delta (YRD) region, and the Pearl River Delta (PRD) region, fog frequencies are impacted not only by climate change but also by fast urbanization and increasing air pollution. In this study, we find that haze days increased markedly in the three regions. However, fog days showed an initially increasing and then decreasing trend, with the turning point in the 1980s; moreover, the turning point occurred 5-15years earlier in large cities than in small cities. We further attribute the long-term fog variations over East China to three factors: regional-scale climate change, urbanization, and air pollution (aerosol pollution). We quantitatively show that urbanization and aerosol pollution contributed at least 1.6 times more than climate change, and their contributions varied with urban development stages. Fog was dominantly promoted by abundant aerosols (45-85%) during the slow urbanization stage, while it was dominantly inhibited by urban heat island and dry island (53-60%) effects during the rapid urbanization stage. In the 53-year period, aerosol pollution promoted fog formation (20-40%).