Lattice effect on magnetic and electrical transport properties of Ln2/3Pb1/3MnO3 (Ln=La, Pr, Nd) films prepared by RF magnetron sputtering technique were investigated. With the decrease of the average ions radius , the structure of Ln2/3Pb1/3MnO3 (Ln=La, Pr, Nd) targets transit from the rhombohedral phase to the orthorhombic phase, and the Curie temperature reduces rapidly with the decrease of . The electrical properties show that films are the metallic state which can be fitted to the formula: ρ(T)=ρ0+ρ1T2+ρ2T4.5 at low temperatures. The temperature range of the ferromagnetic metallic state becomes narrow with the decrease of . The phenomenon can be explained by the lattice effect.