We report on the fabrication of poly(methyl methacrylate) (PMMA) nonlinear optical fibers with dye‐doped cores. The dye‐doped cores have an elevated refractive index that defines a waveguiding region with a large third‐order susceptibility and with single‐mode dimensions. The measured third‐order susceptibility of a squarylium‐doped PMMA film material and the measured optical loss of the dye‐doped fiber core results in a figure of merit that is suitable for all‐optical device applications at &lgr;=1.3 &mgr;m. The impact of further improvements in PMMA loss and chromophore nonlinearity are also discussed.