Dielectric properties of (1−x)Pb(In1/2Nb1/2)O3−xPbZrO3(Zr‐PIN) and (1−x)Pb(In1/2Nb1/2) O3−xPb(Yb1/2Nb1/2)O3(Yb‐PIN) mixed crystal systems were investigated under hydrostatic pressures up to 0.7 GPa. There are striking pressure effects in these systems. In Zr‐PIN (x=0.1) the temperature Tm, indicating the maximum of the dielectric constant, ϵrm′, decreases at the rate of dTm/dp∣p=0=−54 °C/GPa, and the ϵrm′ decreases with increasing pressure, while in Zr‐PIN (x=0.34) the Tm decreases at the rate of dTm/dp∣p=0=−100 °C/GPa, and the ϵrm′ decreases and the maximum value of the tan δ, denoted as tan δm, increases with increasing pressure. For Yb‐PIN (x=0.16) the Tm increases at the rate of dTm/dp=155 °C/GPa, both the ϵrm′ and the tan δm decrease with increasing pressure. © 1996 American Institute of Physics.