Organic thin-film transistors (OTFTs) using cross-linked olefin polymer as a gate insulator were fabricated on a plastic film. An olefin polymer layer was formed by spin-coating and baking at temperatures below 150°C. Pentacene was used as an organic semiconductor layer. The fabricated OTFTs with a short 5-μm-long channel showed a mobility of 0.1-0.2 cm2/Vs and a current ON/OFF ratio of 107. These OTFTs also exhibited good stable performance in the atmosphere. On the basis of the results, we fabricated a 5 inches OTFT-driven flexible active-matrix organic light emitting diode (AMOLED) display. The gate insulator, some metal wirings and electrodes on the OTFT backplane were formed on the plastic film by photolithography. After fabrication of the OTFT backplane, OLED layers were formed by vacuum deposition through a shadow-mask. Clear color moving images were observed on the flexible display even when it was bent.