Abstract: Based on the hourly ozone concentration data accumulated by the environmental monitoring stations in 16 cities during the period from June 27, 2013 to May 30, 2014, spatio-temporal distribution of ozone pollution over the Yangtze River Delta Region was analyzed and characterized. Results show that the annual mean O₃ concentrations in coastal cities were all over 60 μg·m^-3, much higher than those, being below 50 μg·m^-3, in inland cities, and the distribution of NO₂ was just opposite to that of O₃ in pattern. O₃ concentration in the region varied seasaonally, that is, high in summer, and low in winter, particularly in December. In summer, the over standard rate of O₃ concentration was very high, going beyond 25% in 5 of the 16 cities, and in spring it was also high, particularly in Nanjing reaching over 20%. The daily variation of O₃ concentration was a typical "single-peak" pattern, regardless seasons. The lowest value appeared at about 6 a.m. in summer, and an hour later in all the other seasons. The peak value appeared at about 3 p.m. in all the seasons. In summer the peak value might reach as high as 168 μg·m^-3 while in winter the peak value was 85 μg·m^-3.