We report on the magnetostriction of hexagonal HoMnO 3 and YMnO 3 single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction Δ L/L . The measured Δ L/L ( H, T ) data agree well with the magnetic phase diagram of the HoMnO 3 single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO 3 crystal is caused by the Ho 3+ ion; the magnetic moment of the Mn 3+ ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO 3 are consistent with the phase diagram of these compounds. For the isostructural YMnO 3 single crystal with a nonmagnetic rare-earth ion, the Δ L/L ( H, T ) dependences are described well by a conventional quadratic law in a wide temperature range (4–100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.