This study reports the synthesis of ultrafine NiFe‐layered double hydroxide (NiFe‐LDH) nanosheets, possessing a size range between 1.5 and 3.0 nm with a thickness of 0.6 nm. Abundant metal and oxygen vacancies impart the ultrafine nanosheets with semi‐metallic character, and thus superior charge transfer properties and electrochemical water oxidation performance with overpotentials (η) of 254 mV relative to monolayer LDH nanosheets (η of 280 mV) or bulk LDH materials (η of 320 mV) at 10 mA cm−2. These results are highly encouraging for the future application of ultrafine monolayer LDH nanosheets in electronics, solar cells, and catalysis. Ultrafine monolayer layered double hydroxide (LDH) nanosheets with a mean lateral size of less than 3 nm are obtained by the ultrasonic treatment of monolayer LDH nanosheets. Abundant vacancies impart the ultrafine nanosheets with semi‐metallic character, superior charge transfer properties, and electrocatalytic oxygen evolution performance relative to monolayer LDH nanosheets.