A system and method for controlling engine clutch delivery torque of a hybrid electric vehicle when the engine clutch delivery torque is learned includes: an engine clutch configured to control power transmission between an engine and a motor; an integrated starter-generator (ISG) configured to start the engine or to generate electric power by output of the engine; a transmission configured to change power applied to wheels; and a controller configured to control the engine, the motor, the integrated starter-generator, and the engine clutch in a predetermined condition and to check their states under the predetermined condition, wherein while learning the engine clutch delivery torque, the controller operates and controls the integrated starter-generator in order for the engine to maintain an idle speed when the idle speed is varied above a predetermined value.