This paper primarily deals with the examination of the performance under thermal loading of a fire resistant sodium-based geopolymer from Ferronickel slag. In addition, the mechanical, physical and thermal properties of material and their respective variation with time were measured. It is shown that the material presents good mechanical strength and excellent physical and thermal properties. The behaviour of the material on fire was tested by subjecting it to thermal loading with the modification of a standardized passive fire protection test. Two different fire scenarios were investigated: (1) the least intensive standard ISO 834 fire load curve and (2) the most severe Rijkswaterstaat fire load curve. The material behaviour was excellent under its exposure at the ISO 834 fire load curve, showing optimal thermal insulating function and very good structural integrity. Under the Rijkswaterstaat fire load curve, the material showed again a very good thermal insulating function while at the same time suffered from creeping phenomena at the extremely high temperature of 1300°C that affected drastically its structural integrity. As a conclusion, the sodium-based geopolymer from FeNi slag may be an appropriate material for passive fire protection systems under cellulosic fires but inappropriate against more intense fire incidents. Copyright © 2014 John Wiley & Sons, Ltd.