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The characteristics of 45 unconnected upward leaders (UULs) occurred in 19 downward negative flashes observed in Guangzhou during 2009-2011 are analyzed.Each of the 45 UULs is an upward positive leader initiated by a downward negative stepped leader before a new strike point is struck.For each UUL,several parameters are determined when possible mainly by using high-speed images: inception height,inception time prior to return stroke (RS),horizontal distance between the strike point and the UUL’s inception point,two-dimensional (2D) distance between the nearest tip of the downward leader branches and the UUL’s inception point when the UUL is initiated,2D length,and 2D average propagation velocity,whose values range from 40 m to 503 m (number of samples: 45),less than 0.1 ms to 1.32 ms (38),20 m to 1.3 km (38),99 m to 578 m (21),0.48 m to 399 m (45),and 5.79 to 33.8 × 104 m s-1 (22),respectively.Statistical analysis of the UULs’ characteristics shows the following: (1) No UUL with an inception time prior to RS larger than 0.5 ms is initiated at a height lower than 300 m.(2) Those UULs with inception heights lower than 300 m seldom exhibit 2D lengths longer than 50 m,and most (22/27,81%) of them have 2D lengths of shorter than 20 m.Most (12/14,86%) of those UULs with 2D lengths longer than 50 m exhibit inception heights higher than 300 m.(3) Six of the 22 2D average propagation velocities are on the order of 104 m s-1 and 19 (86%) of them are smaller than 2.0 × 105 m s-1.(4) Those UULs with inception heights lower than 300 m only can be initiated by those lightning flashes within approximately 600 m,while those with inception heights higher than 400 m can even be initiated by flashes over 1 km away.(5) The maximum distances for the downward leaders to attract the initiation of the UULs with inception heights from 100 m to 200,200 m to 300 m,and over 400 m are approximately 350 m,450 m,and 600 m,respectively.