  We report results of ultrasonic studies of a single crystal of KDP in the
temperature range 2-300 K. The longitudinal and transverse sound velocities
along [001] and [100] directions were obtained as functions of temperature. The
analysis of the temperature evolution of pseudomoduli $c_{11}$ and $c_{33}$ in
the ferroelectric phase shows that these quantities can be approximated by the
expression $c_{ii}\sim(T-T_0)^{0.5}$ in the temperature range
0.001K$<T_c-T<$0.2K.
