Green fluorescent protein (GFP) molecules are encapsulated by polyvinylpyrrolidone material in the forth of nanofibers to study their diameter dependence of the fluorescence decay rate. Fluorescence dynamics of the confined GFP is governed by the Purcell effect. It is demonstrated that the electrospun nanofibers are quite controllable geometries and are suitable local photonic environments for exploring such effects. The chromophore of GFP, responsible for the intense green fluorescence, is attached to the alpha helix and perfectly surrounded by an 11-stranded beta-barrel cylinder. It is clearly observed that the molecular structures of the confined GFP protein molecules are well protected and are able to maintain their fluorescence properties.