The phase transition behavior of (1-x)Pb(Sc0.5Ta0.5)O-3-(x)PbHfO3 [PSTH(x), x = 0, 0.05, and 0.10] ceramics was investigated by transmission electron microscopy (TEM), dielectric properties under dc bias, and hysteresis loop measurements at several temperatures. TEM showed 5-10 nm cation-ordered regions were embedded in a disordered matrix for PSTH(0.10), which indicated it was a typical relaxor ferroelectric. By fitting the dielectric constant-temperature characteristics, it was found that application of an electric field could induce the relaxor ferroelectric transforming into normal ferroelectric. The maximum dielectric constant of the PSTH(x) ceramics exhibited different trends under dc bias, which was because PSTH(0) underwent the first-order-like phase transition, PSTH(0.10) underwent the second-order-like transition, while PSTH(0.05) lied somewhere in between. The argument was confirmed by the different changes of hysteresis loops above dielectric peak temperature under 40 kV/cm.