Organic-metal chalcogenides (OMCs) are proposed as a new family of two-dimensional (2D) chemiresistive sensing materials. Few-layer Ag(SPh-NH2), one of the OMCs, fully and orderly covered with predesigned -NH2 groups as "receptors", shows the highest sensitivity, excellent selectivity and reversibility in response to NO2 among all the reported 2D chemiresistive sensing materials at room temperature.