Abstract: Surface O3 was monitored at GAW's Longfengshan Regional Station(127°36'E, 44°44'N, 330.5m a.s. l), located in northeast China, from Aug. 15, 1994 to Jul. 31, 1995. Data show that the O3 level at the site was generally not high, though relatively high O3 concent ration (hourly mean>80 ppb) occurred in the first decade of November 1994. Large seasonal variation with the maximum monthly mean concentration (43.2 ppb) in November 1994 and the minimun (27.5 ppb) in January 1995 was observed. Significant diurnal variation always existed during measurement, but the daily O3 amplitude depended very much on the weather and the season. The average daily amplitude was about 28 ppb on the clear days in the summer and nearly 8 ppb on the overcast days in the winter. The relationships between some of the meteorological parameters and the surface O3 have been identified. Wind speed and temperature were found to be positively correlated to the surface O3 level, while the relative humidity negatively. NOx also had effects on the surface O3 concent ration, especially in the colder period when the surface NOx concentration was relatively high. The "gas phase titration" between NOx and O3 could significantly decrease the nighttime surface O3 concentration so that there was good anticorrelation between the nocturnal NOx and O3 concent rations. The daily amplitude was mainly related to the water vapor content, the sunlight time and the UV radiation. Empirical functions of the daily maximum, minimun and amplitude of the surface O3 both in the colder and in the warmer seasons have been obtained using the step-by-step regression. The data calculated based on the functions coincide well with those observed.