Disclosed is a method of estimating a maximum output of a battery for a hybrid electric vehicle (HEV). The method comprises extracting maximum charge/discharge outputs of the battery depending on a plurality of charged states (SOC) of the battery under which the vehicle is able to be driven and calculating an interrelation between them; extracting maximum charge/discharge outputs of the battery at plural temperatures under which the vehicle is able to be driven, and calculating an interrelation between them; extracting degradations of outputs of the battery as a capacity of the battery is discharged during the traveling, and calculating an interrelation between them; and based on the interrelations obtained, estimating a maximum output of the battery using a function.