A series of polymer chemosensors containing naphthalimide signal moiety and imide recognition moiety for the selective detection of fluoride ions (F-) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymer chemosensors display obvious absorption and fluorescence variations upon the addition of F-, which can be observed by both naked eyes and optical responses. The polymers showed higher fluorescence enhancement than its monomer, and the polymers with higher weight have higher sensitivity than those with lower molecular weight. Other halide anions are found to hardly induce any variation of either the absorption or fluorescence spectra.