To provide a denitration method of NOX which can improve ammonia releasing ability of an SCR catalyst in a low temperature region.

In the method where an exhaust pipe for discharging exhaust gas supplied from a diesel engine is provided with a urea water adding means and the SCR catalyst and NOX in the exhaust gas is reduced and purified by ammonia generated from urea water, iron silicate beta zeolite is used as the SCR catalyst.