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A sol-gel-derived film doped with β-cyclodextrin was used to construct a fiber-optic evanescent-wave fluorosensor. In this sensing configuration, the fluorescence emitted was detected from the side surface of the fiber, where the cladding at the distal end was removed. For detection of riboflavin, the fluorescence enhancement by the film coated at the distal end of an optical fiber is 10.6 times than that of an unmodified optical fiber. The enhancement is due to the accumulation of riboflavin in the sol-gel cladding and the more constrained microenvironment for riboflavin. The linear dynamic range of this sensor extends well over 2 orders of magnitude. Detection limit (signal-to-noise ratio = 3) is as low as 80 nM. The sensor is easy to operate, simple to construct, and requires a minimal number of optical components.