Abstract The ultrasmall Ag species decorated on α‐Fe 2 O 3 nanorods photocatalysts are prepared through a facile in situ photodeposition process. The obtained Ag/α‐Fe 2 O 3 composite samples display more outstanding photocatalytic activity than original α‐Fe 2 O 3 in the degradation of tetracycline hydrochloride (TC‐HCl) in water. The degradation rate constant of TC‐HCl over the Ag/α‐Fe 2 O 3 ‐5 sample reaches up to 0.0118 min −1 , which is about 6.21 times than that over original α‐Fe 2 O 3 sample (0.0019 min −1 ). The structure characterizations, physicochemical properties, and photoelectrochemical measurements reveal that the visible light absorption ability and charge separation efficiency are improved dramatically owing to the decoration effect of ultrasmall Ag species on the surface of α‐Fe 2 O 3 nanorods. The photocatalytic reaction mechanism investigations demonstrate that holes, ˙O 2 − , and ˙OH all are main active species and play important roles in the degradation process of TC‐HCl.