A structurally simple colorimetric sensor, N-4-nitrobenzene-N′-1′-anthraquinone-thiourea (1), for anions was synthesized and characterized by 1 H NMR, ESI mass and IR methods. In acetonitrile, the addition of F − changed 1 solution from colorless to yellow. In the presence of other anions such as CH 3 CO 2 − , H 2 PO 4 − , HSO 4 − and Cl − , however, the absorption spectrum of 1 was slightly red shifted with no obvious color changes observed. The association constants of anionic complexes followed the order of F − ≫CH 3 CO 2 − >H 2 PO 4 − >HSO 4 − >Cl − >Br − , which was different from the order of anion basicity. AM1 calculation results indicated that the most stable configuration of 1 existed in the Z–E-conformation with a six-membered ring via intramolecular hydrogen bond. This made thiourea moiety of 1 in an unfavorable conformation to bond with oxygen-anionic substrates such as CH 3 CO 2 − and H 2 PO 4 − , thus leading to a high selectivity and sensitivity for the detection of F − .