We investigated the multiferroicity of the polycrystalline samples Gd1-xTmxMnO3 (0≤x≤0.3) (GTMO) by measuring the structural,magnetic,dielectric and polarization properties.It is found that the polarization increases in slight doping(x≤0.1) samples,reaching up to the maximal value of about 32 μC/m2,and then polarization decreases in the range of 0.15≤x≤0.3 with increasing x,thus leading to a “Λ” type relation.A possible explanation is discussed.