The late immigration of the brown planthopper (Nilaparvata lugens (stl)) (BPH) is defined as mass immigration to the Yangtze River Delta rice areas from late August to early September. It's different from the normal early immigration that happens during late June to early August. There have been unusual abundant late immigrations in recent years, especially in 2005 and 2006. This paper examines the population characteristics of BPH in an attempt to differentiate between immigrants and emigrants, using data collected from field populations and light-trap catches; and also the processes of immigration and its relationships with weather and source areas of the late immigration in 2007 in Shanghai. The results are as follows: (1) The late immigration peak days in 2007, sampled by light-traps, occurred on 22-23 August and 27-31 August. (2) The analysis of horizontal wind field (m/s) vertical velocity (Pa/s) at 850hPa illustrated that the immigration on the nights of 22-23 August was affected by the peripheral inverted trough of the Tropical Storm “Sepat”. During the 27-31 Aug immigration, the frequently changing horizontal air-flow influenced by the Pacific Subtropical High provided the transportation flow for BPH migration, and the heavy rain fall in North and East China caused the immigration of BPH. (3) Trajectory analysis by HYSPLIT showed that the source areas of this late immigration included the southeast coastal rice cropping region in Zhejiang Province (22-23 Aug), the mid and south Zhejiang Province (27-31 Aug), and the north part of southern Yangtze River such as southern Anhui Province and northern Jiangxi Province (29 Aug). (4) The analysis of the occurrence of BPH in Huaining Country, an area representative of the southern rice cropping region in Anhui showed that rice had developed to the mature reproductive stage in late August, so that huge amount of macropterous adult BPH emigrated. The forward trajectories indicated that southern Anhui could be the source area for the immigrants to the Yangtze River Delta. Finally, the relationships between cropping system, population density of BPH in the source area, and meteorological conditions, on the occurrence of late immigration are discussed.