Surface 03 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36 58'37 '' N, 99 degrees 53'56 '' E) in Northeast Tibetan Plateau, China. Daily average O-3 ranged from 21.8 ppbv to 653 ppbv with an annual average of 41.0 ppbv. Seasonal average of O-3 followed a decreasing order of summer > autumn > spring > winter. Diurnal variations of O-3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13-31, 2010 to investigate correlations between meteorological or chemical conditions and O-3. It was found that O-3 was poorly correlated with solar radiation due to the insufficient NOx in the ambient air, thus limiting O-3 formation under strong solar radiation. In contrast, high O-3 levels always coincided with strong winds, suggesting that stratospheric O-3 and long range transport might be the main sources of O-3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions.