In the present study authors examined the sintering behavior on the initial sintering stage of fine tetragonal zirconia nanopowders (containing 3 mol % Y2O3) with and without mechanical activation in a ball mill. The initial sintering behavior was examined by constant rate of heating method (CRH) at different heating rates. We defined a role of the particles surface mechanical activation and its influence on the sintering mechanisms during the sintering of yttrium-stabilized zirconia nanopowders. We found that even a small mechanical action causes change initial characteristics of nanopowdres which can accelerate sintering processes. Increases of milling time causes change of sintering mechanism from volume (VD) to the grain-boundary (GBD).