The natural polymer cellulose exhibits significant potential for various applications due to its unique optical, electronic, and chemical properties. However, the use of cellulose materials in luminescent applications has been relatively limited. This study aims to develop a simple and efficient method to enhance the fluorescence of cellulose materials by incorporating rare earth elements, thereby expanding their range of applications. In this work, we synthesized hybrid cellulose materials by grafting Eu‐bpy (H2bpydc=2,2‐bipyridine‐5,5‐dicarboxylic acid) onto the surface of cellulose fibers through a straightforward post‐processing procedure, resulting in materials with excellent fluorescence properties. By leveraging the abundant hydroxyl groups on the surface of cellulose fibers, Eu‐bpy@CF exhibits high luminescence in response to relative humidity and pH changes, with a noticeable color shift from light red to red visible to the naked eye. Consequently, these materials were further applied in the construction of smart fluorescent switches for the highly accurate and selective detection of phenylenediamine. Our research provides a simple approach to creating environmentally responsive handheld fluorescent papers and expands the diversity of rare‐earth cellulose fibers for developing new fluorescent materials with smart functions. The new multi‐responsive flexible Ln‐MOFs papers were synthesized by simple post‐synthesis method between Eu‐bpy and natural cellulose fiber. The synthesized Eu‐bpy@CF has the highly sensing luminescence performance of relative humidity, pH value and p‐phenylenediamine with high accuracy and selectivity.