The synthesis of a new cationic fluorescent 4-allylamino-N-sulfadiazine-1,8-naphthalimide quaternised with 1-bromopropane has been described. The characterisations of the prepared compound 3 and its intermediates (compounds 1 and 2) were carried out by DSC, FTIR, 1HNMR and 13CNMR techniques. Its photophysical characteristics in organic solvent DMF have been determined using absorption and fluorescence spectroscopy. The newly synthesized compounds have been tested in vitro for its antimicrobial activity against bacteria and fungi. The results obtained suggest that the newly synthesized compounds are suitable in designing new effective antimicrobial preparations.