To investigate the response of planktonic bacterial abundance to lake eutrophication and salinization in drought zones, water samples of 23 stations in Lake Bosten were collected in June, 2010.The DAPI-combined epifluorescence direct counting method (DAPI-FDC) was used to identify the spatial distribution pattern of planktonic bacterial abundance and the relationship with the environmental parameters.The results showed that the epilimnetic total nitrogen (TN) concentration in Lake Bosten was ranged 0.26-1.45 mg/L (mean=0.91 mg/L), indicating a mesotrophic and eutrophic level.The concentration of total dissolved solids (TDS) varied from 219 mg/L to 1696 mg/L (mean=1125 mg/L), which indicated that Lake Bosten is a brackish lake now.The abundance of planktonic bacteria was ranged (1.41-4.57)×10⁶ cells/ml (mean=2.89×10⁶ cells/ml), with the higher values appeared in station 5 and other heavily polluted northwest lake regions, and the lowest value appeared in the station 14 located in the estuary.Cluster analysis showed that the 23 sampling stations can be divided into two groups:freshwater region (FR) and brackish lake region (BLR).Compared with freshwater region, the concentrations of TDS, electrical conductivity, salinity, COD_Mn, chloride and sulfate in brackish lake region were significantly higher.The bacterial abundance was significantly positive correlated with COD_Mn and Cl^-.In summary, the spatial distribution pattern of bacterial abundance was a response to different levels of nutrients and salinity in Lake Bosten.Hence the abundance of bacteria was a sensitive indicator reflecting the eutrophication and salinization.