We report a flexible paper transistor made with regenerated cellulose and covalently bonded single-walled carbon nanotubes. Functionalized single-walled carbon nanotubes (SWNTs) are reacted with N, N-Carbonyldiimidazoles to obtain SWNTs-imidazolides. SWNTs can be covalently bonded to cellulose by acylation of cellulose with SWNTsimidazolides. Using the product, SWNTs covalently bonded cellulose (S/C) composite paper is fabricated and it is mechanically stretched to align SWNTs with cellulose chains. Finally, inter-digital comb shaped source and drain electrode and bottom gate electrode is formed on the paper via lift-off process. Aligned SWNTs can contribute to establishing stable electron channel paths in the cellulose layer. The alignment of SWNTs can be key a role in improving characteristics of the paper transistor. The characteristics of the paper transistor are evaluated by measuring mobility, onoff ratio depending on the alignment of SWNTs in S/C composite paper transistors.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.