Flexible Pt counter electrodes (CEs) were prepared on indium-doped tin oxide coated polyethylene naphthalate (ITO-PEN) substrate by electroless deposition. The correlation between the microstructure and the property of the Pt CEs was investigated. Results showed that isolated Pt nanoparticles were uniformly distributed on the ITO surface at a short deposition duration, and then grew with the deposition duration, leading to the interconnection of adjacent Pt nanoparticles. The interconnection of Pt nanoparticles was beneficial to the electrical property of the Pt CEs, while it was unfavorable to the electrocatalytic property of the Pt CEs. A microstructure model was proposed to explain the correlation between the microstructure and the property of the Pt CEs. In addition, the Pt CEs showed low charge transfer resistance (1.66-0.58 Omega cm(2)), which was comparable to that (1.16 Omega cm(2)) of the conventional sputtered Pt CE. The high electrocatalytic property of the electroless deposited Pt CEs makes the assembled DSCs present comparable energy conversion efficiency of the DSCs using sputtered Pt CE. (C) 2011 Elsevier B.V. All rights reserved.