The cladding of PMMA based polymer optical fibers (POFs) is doped by Rhodamine 6G (Rh6G) in the solution composed of water and methanol. Methanol is added in order to lower the doping temperature compared to that of pure water. Results show that addition of methanol, like raising temperature, can effectively accelerate the doping process. It is also found that there is a critical doping temperature for the solution of given methanol content. Above that temperature, the doping process dramatically impairs the fiber and the fiber loss increases too much for further application. In addition, Microscope observation of cross-sections of doped fibers indicate that Rh6G only diffuses into the cladding. Concentration measurement of Rh6G in the cladding and the core of doped fibers confirms that there is almost no Rh6G in the core. In short, this study reveals that the doping process of PMMA based POFs can be accelerated by adding methanol into water at the same temperature. Most importantly, the solution of methanol and water may be able to dissolve those dopants that are insoluble in pure water, making the aqueous solution based doping method suitable for more dopants. [ABSTRACT FROM AUTHOR]