An ignition system of an engine may include an ignition device that uses the current that is supplied to an ignition coil to generate spark in the combustion chamber, a starting detecting portion that detects the starting signal for starting a stopped engine, a coolant temperature detecting portion that detects the coolant temperature of the engine, and a power control portion that increases the dwell time of the current that is supplied to the ignition coil for a predetermined time after starting the engine, in a case that the starting signal is detected and the coolant temperature is lower than a predetermined level. Accordingly, if the temperature of the engine is low, the dwell time is increased for a predetermined time such that the spark is effectively formed in the cylinder to sable the starting of the engine in the ignition system of an engine according to the present invention.