5-[4-(dimethylamino)benzylidene) pyrimidine-2,4,6(1H,3H,5H)]-trione (DMP-3H), the receptor was synthesized which played a chemosensor role for cyanide ion (CN−) in aqueous solution with colorimetric and fluorescence turn-off responses. Upon addition of CN− ion into the solution containing the receptor, a color change visible to the naked eye was observed from yellow to colourless and also, the fluorescence of the solution was immediately quenched. Moreover, DMP-3H exhibited a selective response to cyanide ion over many other anions such as F−, Cl−, Br−, I−, SO2-3 , OCN−, ClO−3 , CO2−3 , IO−3 , N−3 , C2O2−4 and SCN−. The detection limit toward CN− was 8.1 × 10−7 mol.L−1, which is satisfactory enough for monitoring CN− levels in physiological and environmental systems.