A mu-bis(tridentate) ligand named 2-phenyl-1,3-bis[3'-aza-4'-(2'-hydroxyphenyl)-prop-4-en-1'-yl]-1,3-imidazolidine (I) has been synthesized and scrutinized to develop iron(III)-selective sensors. The addition of sodium tetraphenyl borate and various plasticizers, viz., chloronaphthalene, dioctylphthalate, o-nitrophenyl octyl ether and dibutylphthalate has been used to substantially improve the performance of the sensors. The membranes of various compositions of the ligand were investigated and it was found that the best performance was obtained for the membrane of composition (I) (10mg):PVC (150mg):chloronaphthalene (200mg):sodium tetraphenyl borate (9mg). The sensor showed a linear potential response to iron(III) over wide concentration range 6.3x10(-6) to 1.0x10(-1)M (detection limit 5.0x10(-6)M) with Nernstian slope (20.0mV/decade of activity) between pH 3.5 and 5.5 with a quick response time of 15s. The potentiometric selectivity coefficient values as determined by match potential method (MPM) indicate excellent selectivity for Fe(3+) ions over interfering cations. The sensor exhibits adequate life of 2 months with good reproducibility. The sensor could be used in direct potentiometry.