Temperature dependence of the dielectric constant under the DC biasing field was measured in Pb(Zn1/3Nb2/3)O(3-)8%PbTiO3. The temperature-field phase diagram was clarified in the field range below 2.5 kV. The existence of the critical end point at 172 +/- 3 degrees C and 1.75 +/- 0.25 kV/cm was confirmed.