The long start-up time and large demand of Anammox seed sludge limit the practical application of Anammox process. In this study, the seeding strategy of fast start-up of Anammox process using 2.0 g VSS L-1 of anaerobic granular sludge (AGS) or activated sludge (AS) with various low concentration of Anammox sludge as inoculum was investigated. In laboratory scale, the start-up (achieving 70% TN removal) was shortened from 21 days to 5 days when Anammox sludge concentration increased from 0.02 g VSS L ( -1) to 0.2 g VSS L-1 with 2 g VSS L (-1) AS as inoculum, and 16S rDNA analysis indicated the enrichment of Anammox bacteria, while the start-up failed with AGS. In pilot scale, the start-up was achieved in 10 days using 0.02 g VSS L-1 of Anammox sludge and 2.0 g VSS L-1 of AS, confirming the fast start-up of Anammox process with low concentration of Anammox sludge.