Numerous studies have shown that ecological factor changes along the spatial gradient of urban and rural sites have a strong similarity to the temporal gradient of global change. Therefore, based on environmental gradients between urban and rural areas, a space-for-time substitution experiment called the urban nature experimental field" method is developed to research the response of the terrestrial ecosystem to global climatic change. In recent related studies, the characteristics of ecological factors in urban and rural areas were observed in many cities around the world,most of which were focused on temperature and carbon dioxide. However, some reports showed that the disturbance from near-ground ozone was one of the most influential factors in determining the effectiveness and applicability of the method. To date, little research has been carried out to monitor and identify the spatial variation of near-ground ozone concentrations along the urban-rural gradient. Therefore, we selected the following urban and rural forest sites : the urban site in Qingliangshan Park near the urban center of Nanjing, and the rural site in Xiashu at 41.7 km distance from the Nanjing city center. We monitored near-ground ozone concentrations, as well as light intensity, air temperature and humidity, from June 2011 to January 2013. We also compared diurnal and seasonal variation of ozone concentration. The results suggest that there were significant differences of temperature, humidity and maximum light intensity between the two observation sites (P<0. 001). Compared to the rural forest site, the urban site had an average 0.93℃ higher temperature, 3.37% lower humidity, and 13108.77 lx lower maximum light intensity. This shows typical differences of temperature and humidity between urban and rural sites,and implies the representativeness and appropriateness of the selection of the two monitoring sites. At the urban site, an annual average of 19.95 nL/L in near-gound ozone concentration was observed, slightly less than that at the rural site (23.24 nL/L). The difference pattern of ozone concentration between the two sites varied seasonally. In autumn, winter and spring, significantly higher seasonal average ozone concentrations were observed at the rural forest site, relative to the urban site (P< 0.01). In summer, there was no difference between the two sites (P > 0.05). Relative frequencies of ozone concentrations in excess of 40 nL/L were 14. 0% and 13. 9% at the urban and rural sites, respectively. AOT40 (accumulated ozone exposure over a threshold of 40 nL/L) values at the urban and rural forest sites were 0.968*10 h and 1. 259x 10 h, respectively. There was no significant difference in AOT40 values between the two sites. Our study demonstrated that near-ground ozone concentration in the rural forest was generally higher than that in the urban forest. However, there was no significant difference during summer in the city of Nanjing, the season when plants grow vigorously and are susceptible to damage from near-ground ozone concentrations. We conclude that the disturbance of plant growth from variation of near-ground ozone concentrations between the urban and rural sites was negligible in the urban space-for-time substitution experiments.