Hot indirect extrusion behaviors of fully dense 3 mol% Y2O3-stabilized ZrO2 polycrystals with a grain size of 80 nm were investigated by using a conical graphite die. During early extrusion at 1843 K and a constant compression stress of 60–80 MPa, the relative moving billet velocity (v
0) shows a sharp maximum, followed by a continuous decrease until it reaches a steady-state v
0 value. Visual observations of the material flow by using graphite foil markers indicate that the deformation zone at the steady-state v
0 is well represented by a spherical velocity field. The decrease in v
0 corresponds to the transition from heterogeneous to homogeneous deformation. The stress exponent (n) of 2.07 was obtained from the log–log plots of the steady-state v
0 versus the external applied stress that is compensated by threshold and sliding friction stresses. This n value suggests plastic deformation through grain-boundary sliding in indirect extrusion.