[en] New technologies such as direct reduction and smelting reduction processes are increasingly being used to supplement conventional blast furnace ironmaking technology. The critical product quality parameters in many of these processes are the degree of pre-reduction (PRD) (or the degree of metallisation) and the carbon and silica contents. However, on-line measurements need to be made on hot ore (up to 1000 degree C) in circumstances where access to representative sample streams is very difficult. An on-line gauge based on the measurement of neutron inelastic scatter gamma-rays was installed and calibrated at a plant in Western Australia. The gauge uses an ²⁴¹Am-Be neutron source and a bismuth germanate (BGO) detector inside a water-cooled tube surrounded by hot iron ore. The gauge monitors the iron, oxygen, carbon and silica contents of the ore based neutron inelastic scatter gamma-rays at 0.85, 6.13, 4.43 and 1.78 MeV respectively. In plant trials the gauge determined iron, oxygen, carbon, silica and PRD to within 2.2 wt.% (4% relative), 0.6 wt.% (2% relative), 0.5 wt.% (25% relative), 1.0 wt.% (9% relative) and 0.4% (1% relative) respectively