A new diamine with bulky pendant biphenyl and ortho-position dimethyl structures, 4,4 ′ -((1,1 ′ -biphenyl)-4-ylmethylene)bis(2,6dimethylaniline), was synthesized via a one-pot reaction of 4-biphenyl carboxaldehyde and 2,6-dimethylaniline. The diamine was employed to polymerize with several dianhydrides via one-step condensation under high-temperature conditions. The light yellow or colorless polyimide (PI) films obtained were found to have cut-off wavelengths in the range 286-358 nm and transmittance over 80% in the visible region (400-780 nm). Meanwhile, these PIs possessed excellent solubility in common organic solvents, even in low-boiling-point solvents such as chloroform (CHCl 3 ), dichloromethane (CH 2 Cl 2 ) and tetrahydrofuran. The glass transition temperatures (T g ) of the PIs were determined to exceed 343 ∘ C, even to 456 ∘ C. All PI films were flexible with a tensile strength of 78-119 MPa, a Young's modulus of 2.0-2.5 GPa and elongation at break of 4.0%-8.2%. Therefore, these colorless PIs can be used as candidate materials for flexible display substrates.