  Magnetization and Hall resistivity have been investigated for single crystals
of Dy-doped Nd$_{2}$Mo$_{2}$O$_{7}$. A sharp decrease of the Hall resistivity
upon a metamagnetic transition, perhaps associated with magnetic-field ($H$)
induced flop of Dy$^{3+}$ moments, has been observed in the Dy-doped crystals
only for $H \parallel [111]$ direction. In addition, the sign of the Hall
resistivity at a high field, both for $H \parallel [100]$ and for $H \parallel
[111]$, changes with the Dy-doping. These results are explained in terms of the
sign change of Mo spin chirality that is controlled by the Dy$^{3+}$ moments
with a different sign of $f$-$d$ interaction from the Nd$^{3+}$ moments.
