  We have performed the elastic neutron scattering experiments under uniaxial
stress \sigma along the tetragonal [100], [110] and [001] directions for
URu2Si2. For \sigma // [100] and [110], the antiferromagnetic moment \mu_o is
strongly enhanced from 0.02 \mu_B (\sigma=0) to 0.22 \mu_B (\sigma=2.5 kbar) at
1.5 K. The rate of increase d\mu_o/d\sigma is roughly estimated to be ~ 0.1
\mu_B/kbar, which is much larger than that for the hydrostatic pressure (~
0.025 \mu_B/kbar). Above 2.5 kbar, \mu_o shows a tendency to saturate similar
to the behavior in the hydrostatic pressure. For \sigma // [001], on the other
hand, \mu_o shows only a slight increase to 0.028 \mu_B (\sigma = 4.6 kbar)
with a rate of ~ 0.002 \mu_B/kbar. The observed anisotropy suggests that the
competition between the hidden order and the antiferromagnetic state in URu2Si2
is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio,
or both.
