The layered oxychalcogenides BiCuOCh (Ch = S, Se, and Te) have gained extensive attention due to their low lattice thermal conductivity, moderate Seebeck coefficient, and tunable electrical conductivity. However, the thermoelectric properties of their Ag-based isomorphic compounds are still unclear. Here, by means of first‐principles calculations and Boltzmann transport theory, we identify that three materials exhibit intrinsically low lattice thermal conductivity. Because of large unit volumes and relatively low sound velocities, the lattice thermal conductivities for BiAgOS, BiAgOSe, and BiAgOTe are only 0.63, 0.58, and 0.49 W/mK, respectively. Combined with the analysis of electrical transport measurements results, the p-type BiAgOSe along a-direction shows preferable thermoelectric character with the maximum ZT value of 2.38 at 300 K. Besides, the ZT values for p-type BiAgOS and BiAgOTe at the same temperature along a-direction could reach to 1.75 and 1.90. Our results reveal that the family of oxychalcogenides BiAgOCh is potential p-type thermoelectric material. Especially, although n-type BiAgOCh cannot be a comparable thermoelectric material (ZT = 0.04–0.71), our results imply that optimum carrier concentration for n-type BiAgOS and BiAgOSe could be proved as an effective regulation strategy for relatively large ZT value. This is mainly due to the fact that ZT value has more than one extreme points from low carrier concentration (1 × 1018 cm−3) to high carrier concentration (1 × 1022 cm−3). Furthermore, this finding opens a new avenue for these oxychalcogenides compounds and significantly accelerates the process of the applications in oxides as potential high temperature thermoelectric materials.