A fail-safe device and a fail-safe method for an engine clutch actuator for a hybrid vehicle may facilitate conversion into a hybrid electric vehicle (HEV) mode even upon failure of an engine clutch actuator by diagnosing a failure state of an electric vehicle (EV) mode due to failure of the engine clutch actuator using a pressure sensor mounted on an actuator master cylinder of the engine clutch actuator when a driving mode is converted from the EV mode to the HEV mode, transmitting a diagnostic signal to a hybrid control unit, and allowing hydraulic oil in the actuator master cylinder to be easily supplied into a concentric slave cylinder using a separate emergency actuator when the driving mode is converted from the EV mode to the HEV mode.